This is kind of cute, I hope you keep us posted lol
But indeed, the people more sensible than I have a good point, you don't want to cross a line in a professional/work environment.
But I think there are still options, like asking him if he wants to get dinner or get a drink in a very sincere way, and maybe based on where you propose going (perhaps not just the nearby happy hour watering hole, but a place that would convey you were actually like *meeting up outside and separate from work*).
Another thing I'd say is, if i were in your shoes (well, I would never have gotten this far b/c im awks), but I imagine it would be good to genuinely approach it with the legit mindset that it's a "shot in the dark" type of thing. I know you intend and feel confident you'd simply resume being friendly coworkers, but it's still possible it opens up a can of awkward things like: him questioning himself and thinking what he thought was platonic fun was actually misleading you, or that even if you don't explicitly or overtly behave differently you're internally crushed and disappointed. You know? things like that.
