The phrase "painter friend" refers to someone who is both a painter and a friend. It means that the person is both skilled in painting and also has a personal relationship with you. Full definition
Among my young painter friends he has a reputation for being open, generous, and extremely smart, but I was still a little nervous. (twocoatsofpaint.com)
Then my figurative painter friends talk about their work's abstract qualities. (bombmagazine.org)
I've noticed, amongst my abstract painter friends, that they talk about their work in figurative terms. (bombmagazine.org)