It's interesting that anyone even had to specify that excessive meditation could cause harm. Isn't the whole point of Buddhism to follow the "middle way"?

The problem with "excessive X causes harm" is that it is tautologically true. The real question is the quantitative level where it starts doing more harm than good. Nobody knows, but it's easy to say after the fact that something is "excessive".

Yea, but I think 10 days in a row of 12 hours a day meditation might fall on the "excessive" side, right? I mean, I live in a place where Buddhists are pretty common, and none that I know do anything like that. They might go to a retreat in the mountains, but they aren't just sitting there for hours trying to feel their body parts mentally, they do other things, like copy religious texts by hand or take nature walks to appreciate life.

Yes, but even a traditional retreat in the mountains like you described could be "excessive" to some.