I can offer a bit of perspective on the issues raised, though my DS was a bit younger (3) when he did this a few times on purpose, most likely for attention (he also took a dump in the garden once and said he was pretending to be a dog!)
I didn’t get mad on any occasion, nor did I do any of the OTT things suggested above.
I was just nonchalant about it but made it clear that because it had happened we couldn’t do something nice that I had “planned” for him.
”Oh, that’s a pity- I was going to take you to the park/ for an ice cream/ do some crafts before bed, but I don’t have time now because I’ve got to wash the rug/ clean the carpet/ change the bedding. Never mind.”
That nipped it in the bud quickly.
Incidentally, don’t worry about the night pull-ups at 4 thing. Every child is different.
DS (the same one) was actually toilet trained day and night at 2, but his older sister (high-functioning autistic) is nearly nine and still needs them at night.
As to it not being regarded as normal until the nappy manufacturers brought out pull-ups, this isn’t true either and I can prove it.
I still have my Mum’s old Penelope Leach parenting manual from the 80s (well before pull-ups existed) which says that bedwetting is common up to five and not unusual until past 7 and that most GPs won’t be concerned unless a child is older than 7 and still bedwetting.
It advises a non-scolding approach and to use a rubber or plastic undersheet but also says that there’s no need to take the night nappies away if an older child prefers to wear them.
I hope this helps ☺️