Being pedantic

That's the problem here, though, you're the one trying to be pedantic by referencing how it would be used in relative common speech, versus what was actually done, which is it being discussed in terms of game design.

No "nerf" occurred here, even by your stretch of a definition, because the chests themselves continue to retain the exact same treasure. The only thing that changed is it went from being static to being dynamic. The result of that was unintended by GGG - hence a bugfix.

To be a "nerf", it must have been intended to be that way, and be changed. Anything unintended is, by definition, a bugfix.

The thing is, you're right, uber lab drops are less valuable for a dedicated runner - but it's a bugfix, end of story. The values weren't changed, and like the dev said, only those who noticed it was in a set pattern will even notice the change to the intended way for it to be.

Thing is, value of keys won't drop - now people should be pretty aware it's just RNG. If anything, people were abusing a bug. No longer being able to abuse something unintended is not a "nerf", it's a bugfix, and there's good reason to be specific about it.

If it makes you feel better, you can thing of it this way: while a bugfix can be a nerf, a nerf cannot be a bugfix. It's worth distinguishing between the two, especially when discussing balance.