Why do people think takedowns are not bjj?

I was in a party the other day, talking with a dude I just meet. Someone mention I did bjj and this guy asked me a lot of things, I ended up showing him a video of me competing, and he told me I didn't mention I did other martial arts, cause the uchi Mata is not teached in bjj but in judo, and a double leg I have posted on Instagram is either MMA or wrestling¿?

I talked with him for a while and kinda convinced him that in today's bjj takedowns are part of the program. This incident alone wouldn't be a problem except this exact conversation has already happened to me like 2 other times(not exaggerating) And scrolling in Instagram rells I see a lot of people saying that this or that technique is not bjj.

Do you guys think that takedowns are part of bjj or is it consider another art?

I have only trained bjj and I've been teached takedowns, so I always assumed is part of bjj.