It's kinda both. Mongoloid here used to refer to people with Downs, by comparing them to the (non existent) Asian race of Mongoloids due to both often having eyes with epicanthic fold. Of course I didn't know this when using it as a kid back in the days, and I've luckily not heard it used for ages, but I think all of my peers would remember it if used on a t-shirt.

In France, that would be related to Down syndrome. Technically, in these parts it would be "mongol", with an l, like the people of Mongolia.

AFAICT it's not exactly used against people with actual Down syndrome, but rather as a synonym for "idiot" and the like.