Pictures?

It looks like the same wood (red oak?) but the stain has taken differently, probably because the wood wasn't in identical starting condition. I don't know which is new and old, but residual finish and stain in the old could either darken the floor or keep it from taking up stain relative to the new. The wood may also be different based on where it grew and how it was treated. This kind of situation is why you pay for pros; they just need to keep trying until they get a better match, assuming that's what you contracted for.

They installed the new then sanded down the old. then applied stain to all of it. The new is what looks darker and that’s because it had a lot more grain than the old and so it is darker with the stain. I asked them if we could just add some Slightly darker stain to the lighter boards, or even some of them, to make the change more gradual. They said adding stain would just sit on top and not soak in now, because the other stain was in the wood. Is that true?

Couple of questions:

1. Did anyone test test the original floor for species? There are several types of oak.

2. Did anyone walk through your home to figure out the GRADE of wood you needed to match yours? Select is different from character or common.

3. Did anyone walk through your home to figure out which CUT you have? Rift is different from quarter sawn etc. Each cut has a different presentation of grain.

4. How much was the total job worth? The cost of the wood?

The cut looks different, looks more like rift. Also, as others mentioned, where the oak came from matters. Northern versus southern oak will look different because of the climate it is grown in. Your local suppliers will carry the proper one For your region. It would be odd that they would carry two different ones.

You can tear it out and install rift cuts , sand , water pop then stain. That will give you a more consistent look. Or just resand , water pop and stain For a better match.