What does simstagram pet mean?

It's camera mode for pets, and the pet gains followers (occasionally gets gifts).

Cute! thank you @EmmaVane

That’s nice getting gifts and followers. Didn’t know that. Thanks.

I haven't done it much (still getting into Cats & Dogs because it came out at the same time my mother-in-law died and I just wasn't into playing) but I wonder if it can happen that the animal gets more followers than a human Sim. :D