Malware

you don't need to do anything. just close that page. nothing happened.

It's most likely that the Doctor's web site has been hacked, but you've no need to worry unless you specifically downloaded and installed something from that site.

as William said, the site has most likely been hacked. but there is NO known mac malware that can infect your computer simply by opening a website. the only known mac malware you have to actively download, then open it by hand, then run the program inside by hand AND give it your admin password. it's clear from your post that you've done none of these things so you are quite safe.

Then you're fine.

The Doctor, on the other hand, needs to have his IT people look into the issue or needs to fix it himself if he just had a neighborhood kid setup the site for him. 🙂