I don't know what world YOU are living in, because overweight people, no matter how active they may be, are looked down on like the plague.
1st graders say they would rather lose an arm than be fat.
While obesity may be at an all time high (and it is a sad disease, it really is) I would not say people are more tolerant of it. It is still harder for bigger people to get hired for a job. And, I don't even go there with my Match.com profile. The only "negative" to my profile is that I am not a size 6......but apparantly that is enough for no guys to contact me or return my contact attempts.
As far as overreacting, it might rub me the wrong way. I think the context in which he used the phrase is important. If he was using it to indicate that Henry was morbidly obese, he probably should have just said "morbidly obese." But, it may have just been a harmless statement. Now, if his tone indicated that he finds obesity gross and disgusting and that he looks down upon obese people, yeah, probably a bit insensitive.
I think, really, it is probably okay. Now, if there were morbidly obese people in the class, not overweight, but significantly obese, as in Henry VIII proportions, it probably did make them feel really, really bad. And it was probably not a nice thing to say, especially if there are obese people in the class.
I probably would not have been offended, unless he made it seem like he dislikes bigger people, and then I would worry about how he sees me as a person.