A few people I know professionally (via civvy jobs) have tried to book me, as has an ex-boyfriend. I declined them with no explanation other than I was busy/wasn't looking to take on any new clients. I started doing this long after I worked/dated them, so am certain none knew it was me. I advertise with only a few pictures, none of which show my face. It's was just one of those the things. I know my ex has a very particular type, which I am, so I guess it wasn't really a surprise.
If this guy tries to book you again, decline him, and keep doing so until he stops trying to book you, or else just block him on your work phone. Never, ever mention anything to him. If he has suspicions it is you, do not feed this. And besides, you have no idea knowing for certain that he has somehow found out, so stop this trail of thought and put it out of your mind. However, having been through it myself, it freaked me out for a long time afterwards until I learnt to laugh about it. Even now, much later, I still think 'wtf' before dissolving into a fit of giggles.