For viewers who aren’t as familiar with what “punching” means, the word has is in reference to the boxing term “punching above your weight.” In boxing, when a person tries to fight someone above their weight class, it often is a losing battle.
In the relationship/Love Island U.K. universes, when someone is “punching” in their relationship, it means that their partner could be seen as more attractive, as a better catch, or as someone who is “out of their league.”
Source: https://www.distractify.com/p/what-does-punching-mean-in-the-uk