- a century ago a greater percentage of people were "normal" weight
- human physiology has not changed much over the past century
- our current definitions of overweight/obese correlate with negative health outcomes
I think the classification is largely correct even if you can haggle over some of the smaller details.
(EDIT: That said, people shouldn't be downvoting you just for asking the question, sorry that happened)
With improved nutrition, people are several inches taller than they were a century or so ago.
If the cause of being taller were internal, such as genetic changes: that would be a change in physiology.
I didn't downvote. But if you're asking a question, ask it. Don't phrase it as a statement while pretending it's a question. And if you're making a statement, substantiate it. Ending a question with a period is borderline intellectually dishonest.