Some auto oils are acceptable and some are not.
To top off 1/2 qt, I wouldn't worry to much about, fill'er up.
but avoid the "energy conserving" kinds.
and if that's all there was, change at 1st opportunity which means drive to a m/c shop and drop the oil right there in their parking lot and realy piss'm off.
Otherwise, diesel oils would be 1st choice.