I wondered for a while ..
.. imagine the cat had never been to, or seen the basement before. Then on that day, it discovers the basement, full of crap and garbage, for the first time. It suddenly realizes the humans are not the gods it had thought they were, but just creatures like itself, and goes totally beserk with rage.
Of course, that cat had surely visited the basement millions of times already, and your explanation is the only possible real one. It had to be due to some type of toxic chemical.