Boys do take longer to develope the ability to go through the night.
I found with my son I brought theses night pants (we use to stress they were not nappies, so he didnt feel like a baby). Then the stress they go through wetting the bed is taken away. When my son was able to go a week with dry night pants he stopped wearing them and he never wet the bed from then on. He was 6 years old.
But this way there was no fuss, no stress, he did not think anything was wrong and now he is fine. Tell this mum not to worry, I have seen night pants upto 14 years old, so that tells you something, he will develope in his own time we are all different.