Are lap trays on wheel chairs considered restraints?

Yes.

I don't see why. They are just a little table. Helps to hold a book, a drink, etc. Don't see where there is any restraint.

I don't know about where you live but my grannies had one in NV nursing home and it was never a problem. It kept her from sliding out of wheelchair and without it she would have been bed ridden. It was made of a foam rubber type material.