Can someone clarify the rules on this?

[cornej1]

Hello Everyone,
I'm new to the forum and joined specifically to see if someone could clarify something for me that's driving me nuts. First, I played football through college, am an avid fan, coached youth football for many years, etc. I generally understand the rules. My son plays on a D3 college team here in the Midwest. At his game on Saturday there was a 3rd and 15 play where the refs called an ineligible receiver downfield on the offense and then called pass interference on the defense. After a little discussion they picked up the pass interference flag and ruled the pass un-catchable. Our coach then declines the ineligible receiver penalty to bring up 4th and 20, right? I believe the ref actually announced it that way, but we then had another long discussion amongst the refs and ultimately re-played 3rd down. I actually saw the down marker guy flip to 4th down and then had to flip it back to 3rd. How does that scenario not bring up 4th down?

Thanks.

Jason