Probably the most logical reason is that it just incubated for a shorter time - let's say 12 hours or less instead of 24 hours... Or whatever the time frame may have been. So there's going to be LOT's of lactose in it.
I know (or am petty darn sure) you've been off milk for some time - and because of all the lactose in it, and I'm guessing you had yourself a decent helping of it. Soooo.... this = the runs! Probably in a major way.
Also what did you use for starter? If it was anything with lacto bacteria in it this can also cause the runs in a big way if your system isn't used to it.
I only say this cause I've been there before, haha...
EDIT: When I make cow's milk or goats milk yogurt I use full fat or ummm 3.5% or even un-homogenized milk. The results is always nice and smooth, even for low fat milk. Chunks or slightly chunky will for sure have you in the can as well... haha. I missed where you said it was chunky! But It won't kill you... or shouldn't ;) Make a new batch and let that one get outa your system. I flushed myself with lot's of water... lot's and lot's and lot's and lot's of water. Seemed to help from what I recall. Was a while ago though.
Post Edited (Canada Mark) : 3/10/2014 11:46:26 PM (GMT-6)