Jawrgy, you need to find out how much oil is in the engine; wipe the stick properly, and reinsert it. pull out and check.
If it's above the low mark, you're ok, but I'd still put some in. If it's just that drop on the end of the stick, add 1/2 a litre and see where you end up. If still nothing, add another 1/2. Take your time there's no reason to hurry. I'm assuming you've got some 10w/40 oil handy?
You'd be amazed how much oil you can pump out through a dipstick, but by the same token it's amazing how much of a mess you can make with 500mL of oil; once it's sprayed around.
They're a hard engine to check once they've been running, as they hold a lot of oil in the heads etc, and it takes a while to run back down. I always check mine first thing in the morning.
If you're not sure though, please don't drive it; better to wait a day, than destroy a perfectly good engine.
Good luck, Dale.
P.S. After the weekend I d be dropping back and telling him what happened, and getting him to dump the mixture of oils out, refill, and steam clean your engine bay. It's the least he can do.