They already knew of the arrangement between George Weasley and Harry Potter. Due to George being Count Ambassador Arthur Weasley’s son, and Harry still remaining loyal friends to Hermione, the pairing was approved and the signed blessing for them to have one groom and three brides after Harry and George were both under the Potter name. In George’s mind, there will always be the Weasley name, and the Potter name needed to be expanded, so it made sense.