My child graduated from an LAC with fewer than 2000 and had a great experience. She didn’t do sports, theater, or music in college. There are still plenty of students to meet, and not doing any of those things doesn’t preclude your child from becoming friends with kids who do do those things.
Remember, the big advantage from the get go is that kids at a small college deliberately CHOSE that environment. They already have something in common.
I suggest just letting your son see if he likes the vibe, and not worry which kids are athletes and which are in theater. By the time my child graduated, she had friends who did many things she never ended up doing. She did other things: she joined debate, worked campus jobs, volunteered, etc… Those are all activities too. And may of these students try all kinds of things that other kids may not try. So my D never did theater, but her friends never tried knitting or taking Chinese cooking courses. All these differences help keep things interesting.