Just be thankful the curtain hasn't moved (yet).

The person who chose 4E has no way of knowing that a couple travelling together chose 4D/F.

Reminds me of a recent flight where a couple in 12A/C kicked up a fuss because someone was in 12B, and they claimed they were told the middle seat would be blocked as they were BA Silver.. Then they asked to be reseated with a free middle seat, the crew told them they could have the back row and they declined!