I agree, it would mostly be a
PR mechanic. I think a simple explanation would work too. Have the HL look at the chains, "yep, it is short of the tape mark so we won't have a first down." Explain that to the coaches (if necessary) then walk the penalty off. I don't even think it needs to be said directly to the coach. It could be a general comment, "since we are short of the five yard mark on the chains it will not be a first down" or something along those lines.