It was grainy and dark grayish-red, quite spicy
Yes.沙 茶酱 (shā chá jiàng) Shacha Sauce.
The 沙 means 'sand' referring to that grainy texture you describe.
6 hours ago, shain said:I had the tiniest nibble of this blood cake (it was duck's I believe)
Could be duck blood, but pig's blood is more common.