Maybe the previous owners consider him retired AND want someone to know that when they look up the info. This would definitely cause me to investigate further, even contact the owner who marked him retired. It may not be fishy, but it's definitely worth investigating, just in case something's amiss.
When you renew your membership each year, you are asked to select the status of each horse recorded in your name. I have a couple horses, for example, that I still own but no longer plan to compete on so they are listed as retired. They are no longer of competition use to me, but if I did end up parting with them (which I don't plan to) I could imagine a situation where a new owner might want to show them at a lower level. There are all kinds of situations that would bring a horse out of retirement. I'd ask the owner. Simple as that.
I listed 2 horses I no longer own as "Retired" this year, as otherwise they ask for you to put in the subsequent buyer's info so that they can transfer the life membership without a Bill of Sale, etc. I was too lazy to look up the subsequent owners' info, I gave the horses to friends, and there was no other suitable "option" on the USEF website this year. The horses are alive and well, but not currently showing.