So, I did it again: bought some yogurt that turned out not to be yogurt, or at least I think it isn't. I'm not very confident in my yogurt knowledge these days.
Here it is:
I've bought something in a jar like this that very clearly IS yogurt, but when I checked an old jar I noticed it said "Yaourt" on the side (or however you spell yogurt in French; I always have trouble with that one). This has a very, very thick consistency and didn't taste at all like yogurt.