Is a 4K Upscaling blu-ray player an UHD blu-ray player?

It's still a blu ray player so no.It wouldn't play the 4k discs.

Maybe.  Not enough info.  

4K is often used to refer to UHD (even though that is not precisely accurate).   Blu-ray discs can standard HD video encoded on them.  Ultra Blu-ray discs can have UHD video encoded on them.  The term "4K upscaling blu-ray" to me means it plays standard Blu-ray discs and uses graphics processors to scale the HD from the Blu-ray to produce a UHD output--which, if done well, can actually look better on a 4K/UHD display.  That statement, however, does not guarantee that it can read the 4K encoding on Ultra Blu-ray discs--if that is what you are asking.  These most players these days that output 4K/UHD will also play Ultra Blu-ray discs.  Look for the phrase "Ultra Blu-ray" in the title or description of the product.  Many of these plays can also stream 4K from Netflix, Amazon Prime, and many other streaming services.You also want to see the acronym "HDR" (or even better "Dolby Vision") if you are buying a 4K Blu-ray player, particularly if you have a TV/display that supports it.