What about if you still go for the 1080p? Does it look ok?
Its a TV, check the settings, sometimes TV's dont have the proper interface installed for this case and/or the firmware is not uptodate for this to recognize things properly, therefore signal to the card that it has only 720p, making your OS think its recommended, because its based on that information the TV sends (roughly said).
50" 1080p will have a pretty stretched pic tho, the distance between each pixel is greater (lower PPI(pixel per inch)) , so youll see black lines if you go to close, keep this in mind. TV's arent really meant for plugging with a PC most of the time.
But if its working, ignore the recommendations?
Those are pretty complicated things in detail, so dont think much of it, just know that not all TV's are 100% supported by OS/GPU companies, especially the 1080p on that high inch screens..