Kids do this.
They are kids.
No kid, is accident proof. No kid, even if being potty trained, will be accident proof.
No kid, is 100% perfect about it everyday.
Childhood.
My daughter, even at 7 years old, had accidents.
In Preschool too.
She was potty trained at 2 years old. By HER readiness.
Still, accidents happen.
Also, kids this age 'think' they can hold it longer than they actually can.
ALSO, night time dryness, is not something that is biologically attained, until even 7 years old. Normal and per Pediatricians.
Night time dryness, is a whole separate process, than day time pottying.
It is about the biological maturity and development of the organs. Not the child's age.
Your child is normal.
Put it this way, my Daughter's Preschool, Kindergarten AND 1st Grade Teachers, ALL said, that kids these ages have accidents. Thus, in these grade levels, they ask the parent to bring extra clothing to keep at school. Just in case. Even the Teachers do not make a big deal of it.
I know, I asked them.
And I asked them, because, my Daughter at these ages, had accidents.