Yep, this. You don't hire interns, grads, and juniors for remote work. So automatically the average salary is higher for remote work when you limit it to mid level and above.
Right, and in my experience at least a lot of remote workers are not people who are hired for a remote job but a senior(ish) person who negotiated with their employer to transition to being full-time remote, even if the company doesn't explicitly allow or support remote work.