[Austen]

Hi there, welcome to MLMF!

He says it's the way the valves end up when the engine stops, letting some oil seep down on the piston, which burns off on the initial startup. Does this sound correct?

That would be correct. As long as it's not doing it everytime you start it up or is burning oil, it's considered normal. My STX does it every once in a while along with our Honda mowers. I think that it is just a common thing for small engines to do. No worries.