Oil light on

I went to look at the car I’m trying to purchase and it looked to be leaking from the oil filter and the red oil light was on. the guy said his brother change the oil but put the filter on wrong. could that be why the red oil light is on?

If the red light is the oil warning light then yes it could be on because of the filter being installed wrong and it leaked enough oil that the pressure is now gone. I wouldn't buy it until the filter is replaced and not leaking and you can verify that the low oil pressure that turned the light on didn't do internal engine damage.
It doesn't take very long for a lack of oil to do serious damage to bearings and camshafts.
If they were running it with the light on then I would pass on it because now you don't know how long it was run that way and it could become scrap at any moment.
Now if you owned it I would tell you to put a pressure gauge on it and see what the oil pressure really is, but as you don't it should be up to the seller to get it repaired before sale.