are you sure he didn't have a fever? usually "call me at work if he seems sick" is parent speak for "I know he is sick, i gave him tylenol and am hoping you deal with it so i can stay at work as long as possible". Really he probably should have been home for the last several days but I definitely would have called right after the first liquid poo. Parents blame a lot of things on teething. Here is a reliable list of what teething does and does not do.
http://www.mayoclinic.com/health/teething/FL00102
Teething does NOT cause diarrhea