Games : Is there a way to hide a steam game from your recently played list?

A friend of mine said he's seen me playing a game on steam while I was at work. Since he only has two friends in his list I tend to believe him (ruling out a mix-up)

But the game does not show up on my recently played list. Is there a way to play a game without appearing in that list or to delete an entry?

Just to be sure, I changed my steam password.