It's quite possilbe if you had it directly after training and it was just too much (and too thick...not enough water or dilution) that was the main culprit. Sometimes cheap whey concentrates can disagree with people (lactose intolerant?) especially if they aren't mixed with enough water or something. But right after you workout something too heavy in the stomach can sometimes cause this. All the blood you need for digestion isn't there. Like Monta said, the trick is lots of water.
But I've had episodes just from my regular tried and true post workout shake for whtever reason. Sometimes it's just a bad day
