Fresh Air Intake Vent Smell

I dropped something on top of furnace in basement. When I reached over to get my nose went across vent in picture. Smelled slight gas. Heater hadn’t come on for about 2 hrs. Had local hvac friend look at it and couldn’t find anything wrong but did notice the slight smell as well. He didn’t do any elaborate testing though. He said it could be gas valve inside furnace not closing all the way leaving some residual gas smell if anything. Or could just be residual gas from the unit running. I’m looking to see if anyone has seen this before ? Leaving gas off. Could it be internal gas valve? Or heat exchanger? Or just residual smell from unit. Links to pics below. One is the vent I smelled gas through. Other are the tubes I was talking about.

https://imgur.com/cSBX783

https://imgur.com/1OWrVAA