TIFU by nearly running over my dad's mechanic.

So my dad's truck started to spill water the other day and we weren't sure if it was the radiator or the water pump. So we contacted our mechanic. He's kind of an asshole and we even have a name for him "mentiras" (Spanish for "lies") because when he says he is going to show up he doesn't and then randomly shows up on a day we weren't even scheduled. So anyways he showed up yesterday after he said he couldn't and my dad wasn't home, then he showed up today and my dad was at work but I was home so we were able to look at the truck. He asked me to turn it on, please note that I have no experience whatsoever of the manual transmission besides turning on a mt vehicle, and when I did I let go of the clutch and the truck moved while he was in front of the truck looking at the engine. What surprised me was that he wasn't as upset as I thought nor did he tell my dad who arrived like 20 minutes after. But yea the truck moved about a good foot and he didn't fall back but it did give him a good push.

TL;DR: I have almost no experience driving a manual transmission vehicle, mechanic asks me to turn it on, I let go of the clutch, truck moves about one foot while mechanic was in front looking at the engine.