We got much the same answer, although we were only refinishing. Pretty sure our builder went with the cheapest he could find!

Many people prefer white oak because it has less of the orange tone than red oak. It's probably impossible to match what you have exactly, so going with all white oak is good advice.

I do not see any mixed species, only red in your photos. Can you post a wide shot, along of other areas?

Thanks for the feedback. I have a hard time seeing a mix, too. Here are some additional pictures.

Here are pics of the boards he scraped and sampled. They were all on the edge, where a wall was removed. I’ve also included a photo of the test samples.

I see there have already been some pieces replaced in at least one area. Its possible, that someone patched those pieces in and used white oak. They appear to have taken the stain a lot darker than the rest of the floor. The rest of the floor looks to be red oak. I see at least 3 shorter boards that have been laced in as a replacement on the wall side. I would use red oak, for the rest of the floors, and since they will all need to be refinished to match, have them remove those 3 boards and put in matching oak there too, so you dont have those strips of very dark wood.