Rapid strep can definitely be done in a pediatrician's office. If they've been tested and they are on antibiotics, they can be around people after 24 hours iirc. We had strep this summer. No fun.

If they are just assuming it's strep with no treatment, I'd side eye that a little.

It can be difficult to tell the difference between a normal viral upper respiratory infection and COVID, especially in children (who are often completely asymptomatic). In general, COVID causes less nasal congestion, sneezing, and drainage and more sore throat and fever when compared to a normal URI. But that is a huge generalization. Strep tests are notoriously inaccurate. A lot of kids are also Strep carriers, and they will test positive even if they are not sick. It is, unfortunately, a dilemma. Will give reference:
COVID-19 in Children and Teens
Good luck.

If you want the real medical nitty gritty it is called Centor Score for strep:

https://www.mdcalc.com/centor-score-modified-mcisaac-strep-pharyngitis