Best bet is to either take it somewhere for a pressure test or let it idle and hunt the leak yourself. How long does it take for the puddle to form?

This isn’t really a diag, because I can’t do it over the internet, but it does sound like brakes were possibly holding. It has phenolic pistons that like to get tight and hold pressure, but sometimes act fine. There should be other signs that the brakes were hot though, edges of the rotors being a brick red color, white edges on the pads and such. Maybe take it somewhere else and have it checked for a second opinion.

Also any chance you had the parking brake on by mistake?