The technology that's being used in the cited article won't result in a transgenic food (ie, a so-called "frankenfood"). They're not transferring genetic material from one organism to another, they're identifying and suppressing one aspect of the existing plant; whether that be kale or anything else. It's the equivalent, at the cellular level, of picking the seeds out of your grapes (and of course, we've successfully bred grapes to be seedless without us doing it manually, which arrives at the same end by a different process).
If the plant was not carcinogenic to begin with, it won't be carcinogenic afterwards.
