5 seconds of air exposure will not effect how sterile anything is. I wouldn't put the plunger on the counter or anything.
Also, nobody said anything about reusing a pin twice, or to use the same pin to inject that you use to pull from. He only suggesting pulling with a larger pin and injecting the oil into the end of a briefly opened slin pin. If you do this without touching the pin or plunger against any object, it's not going to alter sterility.
With that being said, I usually warm my oil up under warm water if I'm going to pull with a slin pin. I don't mind it taking a minute or so to pull. Slin pins are super easy, I can shoot anywhere with them, even sub-q, when it's less than a CC. Completely fine to do this.