I could have used it I guess as I don’t know the gender of it, but what’s wrong with things? I love animals and I didn’t mean to use it in a derogatory way.
in this case, thing isn't derogative to a native speaker, in my opinion. I can see where your confusion is, though.
my tip would be to look at the other words in the sentence to try and grasp the tone of the entire statement. I know it's difficult, but you'll get there... good luck!
Thing is a synonim of stuff and they don't really have any kind of different connotation. Stuff might be more coloquial, which doesn't mean thing is formal, I wouldn't use stuff in a form setting, that's all.
I just today watch an episode where someone said "you are the thing I love most" to a person as if it was a sign or something but it's just selective memory.
I'm sorry for being stupid I guess. We are all here to learn.