Swiss Pairs, MPs -> VPs
4♥ was alerted (incorrectly) and explained on request as a splinter, agreeing spades.
Result: 5♦X(E)-2, NS+300
The regulations state that no bids (other than conventional opening bids) should be alerted above 3NT.
I was called at the end of play when it was found that the North hand did not match the description. I asked NS what their agreement was about the bid. North said that the explanation was correct and that he had misbid, but although there was plenty of evidence that they play splinters in other situations, there was none on the convention card for this situation specifically. South volunteered that he expected his partner to bid 3♥ then 4♥ with the hand he had, so he supposed a direct 4♥ was a splinter.
East said that had he been told that 4♥ might have been natural he would have passed. When asked why, he said it is more likely to be right for him to carry on bidding when the opponents have a known fit rather than a probable misfit.
Apart from telling South off for alerting, what would you do as TD?