First time poster here. Would appreciate any input. We recently had the hardwood floor in one bedroom sanded, stained and sealed with water-based poly due to issues with paint splotches and ridges after removing a built in bookcase. The finished product has several uneven spots (please see photos). There are several spots along the baseboard as well as in the middle of the floor that look blotchy. Despite this being a fairly small bedroom, there are at least 10 spots. The contractor believes that one of the previous homeowners had an animal that had accidents all over the room (a cat perhaps?) even though these spots weren’t there before the sanding/sealing. I am skeptical of this because the floors were refinished before we moved in about 4 years ago and there are no spots anywhere else in the house. The contractor says he will resand, restain and reseal (but will use oil-based poly this time) but there is no guarantee it will change anything. My questions are this:

1. Do you buy his explanation for the uneven floor spots? If not, what could be causing this?
2. Is this fixable? And if so, will the oil-based poly solve the problem?

https://ibb.co/GCQcSHf
https://ibb.co/FbHT6qB

If it’s relevant, I believe that the sanding and sealing all took place in one day. Thanks in advance for any help.

Perhaps this is tannin pull from how the finish was applied. Water-based finishes can lift the tannic acid that is in the fibers as the finish sits on the floor before it is spread. This is not from any kind of pet stain. I think that over time the color will even out. Light will affect the wood developing a patina that will make this difference in color not as noticeable. It should't be much of a bother as you will have furniture and differences of shadow and light in the room as you live in it.
This will not affect the way that the finish will protect the floor from wear.
If you would like to go through the finishing process again, oil based finishes do not lift the tannic acid and there will not be differences in color by the way that the finish will be applied.

Thank you for the input and advice! Much appreciated.