I usually ask a mom-pop butcher down the street to use their vacuum-chamber machine to seal my bags after I fill them
I think not having any sort of vacuum machine to experiment with puts you at a disadvantage when talking about the real world effects of some of the science involved.
“We can broadly define cooking sous-vide as heating the food previously sealed in an airtight and heat-resistant container whose atmosphere has been modified ( a vacuum has been produced,, with or without elements such as gases, liquids, etc.).”
It appears to me that they might be using the term "Atmosphere" in an inconsistent way in their book and this is causing confusion. In general with SV when you change the atmosphere you are reducing the oxygen and not creating a vacuum state. SV is often associated with MAP (Modified Atmosphere Packaging). You see MAP all the time in grocery stores. In all cases the package is sealed (and may even be lose fitting) but has a cavity of some form of gas (normally Nitrogen 70% and Carbon Dioxide 30 %). Lots of fresh pasta and more and more meat trays are packed this way. MAP extends storage life by removing oxygen. Often the contents of the packaging is fragile and would crush if you removed the oxygen by removing all gases (berries, chips, baked goods etc). Instead of removing the gas void in the packaging like vacuum sealing the manufacturer just replaces (or in some cases never introduces) oxygen in the packaging. In the food packaging industry "atmosphere change" means to make a change in the normal composition of air (78.08% nitrogen 20.96% oxygen 0.03% carbon dioxide). It does not mean pressurize of sustain under vacuum. A vacuum sealer does change the atmosphere of the packaged good by removing or changing the composition of air before sealing and returning the packaged goods to normal pressure.
”6. In sous-vide conditions, water vapor forms at much lower temperatures than in normal atmospheric pressure conditions.”
At 20hg vacuum water boils (vapor pressure) at 157 degrees Fahrenheit. If you were cooking something in a rigid vacuum chamber you could boil water at room temps. The problem with the statement from the book is that you don't have a vacuum in the bag outside of the vacuum sealing chamber so you have not lowered the vapor pressure point of water.
Say you are using a chamber style vacuum sealer. For this example let's say that the vacuum sealer can pull a vacuum low enough to boil water at room temperature. You put a vacuum bag in the sealer and add some water. You close the sealer and pull vacuum until the water in the (currently unsealed) bag starts to boil. You can see this through the clear top of the vacuum sealer. You now seal the bag in the chamber and release the vacuum. You take the bag out of the vacuum sealer and put it on the counter. Is the water still boiling? Why not?
Imagine that your vacuum bag material is very thin. Take a small air filled balloon and measure it's circumference. Put this balloon into the bag and vacuum seal it. Take the vacuum sealed bag out of the sealer and measure the circumference of the balloon inside the bag. Is there a difference? Why not?
Put the vacuum sealed balloon into a vacuum chamber and draw a vacuum. Does the circumference of the balloon change? Why?
Even if you do lower the vapor pressure of water in a rigid sealed container you still need heat to "cook". What if you are boiling water at room temperature in a vacuum and put a raw egg in the water. How long do you think you will have to boil the egg until it's hard cooked? That said using a vacuum to reduce a liquid can have a really nice effect, but in this case the vapor needs to be evacuated out of the vacuum chamber. This sort of reduction can be done very easily at home with a $10 aspirator and a rigid container.
“Sealing in shrink bags: guaranteed pressure”
Yes. If the bag material is elastic and designed to shrink using heat it is possible that this could add more pressure to the contents of the bag than what is normally present at normal pressure outside of the bag. Very few Sous Vide bags do this however. This will mostly be things like Cryovac brand material. To be sure there is no vacuum inside the package when the package material is essentially squeezing the contents. In reality its also really not that much pressure.
My soup looked like an above ground pool in a bad neighborhood.