Although, as you say yourself, the pipeline was already shut down. US had much to gain, but surely they would wait until it was opened up again before taking such drastic action?
Also, the diplomatic consequences are pretty dire when Western Europe works out that their ally has blown up one of their major energy supply lines.

Biden's comments could easily have been aimed at the diplomatic pressure that the US could have put on Germany & co. Although maybe behind closed doors that pressure wasn't bearing fruit...who knows.