Yes.

When I tried to read the book, it seems to have activated some kind of spell. Before I knew it, this cat was sitting in its place.

Hmm. A magical creature using the grimoire as a core, perhaps...?

That would explain it, at least.

Since you triggered the spell, Patchouli, your temperament must have affected the cat's appearance as well.

It does not. That's the part you're wondering about?