To answer the obvious question, no payment was made to post or download the photo. These royalty-free sites have millions of images hosted and may make money from creators by selling the rights.
1,000 downloads though. That photo also has almost 80,000 views and achieved front page status on Unsplash.
Anyone can open an account and upload their own stuff. Unsplash will check every image (using tech presumably!) to make sure it fits within their guidelines.