Can pvcs cause a low oxygen level on a pulse oximeter? it stays low for a few seconds and jumps back up. or is it likely a finger pulse oximeter error?

Both: The machine works by detecting a regular pulse and then calculating the oxygen saturation of the blood cells by percentage. If the machine is not able to follow a regular pulse, the number it displays usually goes lower and then stops displaying (or displays an ERROR symbol, etc...). Note that oxygen saturation does not equal the quantity of oxygen in the blood, but that's another story.