The oil filter cap does not need to be really tight. 25Nm I think. It is written on the cap!
I know on my car - when I tighten the oil filter cap... the green marks almost line up. They are off by 15mm's or so - past when they aligned up new.
Normally you want to hand tighten the oil filter cap and then turn it with a cap socket/wrench another 1/4 turn. But I go more by feel then anything else. It really does not need to be too tight. You might want to remove the cap and use a floresent light to check for any cracks in the oil cap.
I think I would also check the oil drain plug for tightness. You might as well - re-due thier oil change. That will be the
ONLY way to sleep at night! I know that is what I would do!
Did they remember to put the oil fill cap back on (on the valve cover) as well?
Good Luck,
Dackel