No, you have wood veneer over particle board with wood edge banding and backer sheet.
You have to be careful if you are going to sand /refinish as you don't want to (you most likely will) go through the veneer. Veneer can be 1/16 to 1/8 of an inch thick.
Method 1 remove a drawer, go into the cabinet and drill or sand the under side of the counter to see if it's solid.
Method 2 do a test run somewhere inconspicuous like behind the toaster. If it's veneer you can patch it with an iron on patch and it won't matter too much.
Well, my kitchen has a similar corner and it has a cupboard with turning pull-out shelves which make use of the dead space that you have.
So consider taking the nearest cupboard out then dealing with the holes and putting better cupboards back in.