2000 a month is not enough to live on (California), but it's also not nothing. It's a pretty serious amount of money, especially if it's given per month. For reference, the median salary in California is around 4000 per month before tax (according to US Census). If we assume that he is an average person from California, then he is giving you 50% of his entire income. He's left with 2000 a month himself, which isn't enough for him to survive. And California pays well, so if he's not from California, then he's likely sacrificing a lot more than in this example.

As a general rule of thumb, a single person's salary in America typically cannot support 2 people, so even if he's "only" giving you minimum wage, it's still a very substantial amount of money. Also, 2000 a month is almost double of what you earn on federal minimum wage, so what your friends say isn't even true.

Honestly, my read is that your friends sound problematic. It's minimizing and downplaying his contribution and sacrifices, even if it's meant to be a joke.