Kids have accidents.
It just is.
It is childhood.
Even if they are potty trained, kids have accidents.
It is not necessarily a regression.
Their body is still developing... physiologically.
They have accidents.
ALL of my daughter's Teachers, from Preschool to Kindergarten to 1st Grade... ALL said this. Kids these ages, have accidents.
They are not 100% error free, even if they know mentally in their heads.
Your child, is very young.
Also keep in mind, that night time dryness is a whole SEPARATE thing from day time toileting. Night Time dryness, does not occur, BIOLOGICALLY, until even 7 years old, and this is NORMAL and per Pediatricians too.
You cannot 'train' for night time.
It is biological.
At about 3 years old, in already potty trained kids, this is the age when hiccups, occur.
Their brains and biology, is not synchronized..... or they THINK they can hold it longer, but can't. They don't know how long they can hold it.
Kids this age, do not yet have, accurate ability to 'gauge' how long they can hold their bladders.
This is typical at this age.
Even for my daughter when she was that age.
MANY kids at that age, they mis-cue, how long they can hold their bladder.
No, don't scold him.