Correct me if I’m wrong but my understanding is that equal pay needs to be for the same job. In this case the argument seems to be that the jobs are not the same, but that they are similar, it seems to be a grey area.
The article states that just over half the warehouse staff were male and that over a quarter of shop front staff were male, so it doesn’t appear to be a case of “they’re getting paid more because they’re men”.
Presumably any of the women in the shop front could have asked for a transfer to the warehouse?