AITAH for flapping my arms like my autistic little sister despite not being autistic myself

I have a little sister who is the world to me. She really is my everything. And she does this thing called stimming where when she gets happy she flaps her arms like crazy it’s so cute. I started copying her a few years ago and she loves it. I have even started flapping my arms out of joy when she’s not around to see it, just muscle memory I guess. But recently my friend who is autistic and stims (though on a different way) has called me ableist because I am not autistic and I am appropriating autistic behaviours. AITAH for doing this?