We recently purchased a home with wood floors from the 1930s. They were in good condition but didn't need to be sanded and sealed.

the floor guy is almost done applying duraseal and when I went to go look at the floor today I saw a bunch of big circular areas on the floor. What happened here? Is this recoverable? See the pic...

https://photos.app.goo.gl/aFnB8os7ZiCqvGop6

those look like stop marks for a Floorboy - its a small buffing machine. The fellow who did the work stopped the machine to either refill or take a smoke break maybe. I used to run into that sometimes when oiling floors. Depending on the product used, you may be able to buff those marks out. Whoever did the work should come back and correct this for you.