I'm not sure if the cleaners did anything to it. I hadn't noticed anything wrong with the sweater when I got it and I've worn it several times (and I've never really had trouble with their sweaters except for the pilling) but I find it strange that it came apart at the stitching.
If by "bar fight" you mean taking it to the cleaners once and then wearing it a couple of times then, yes, I was in a bar fight. I do see that the QC varies quite a bit. However, I'm not sure how J. Crew compares with other stores.