It doesn’t seem likely to me that someone would commit suicide in a dumpster.
From the TEXT to his mother, he had a very low opinion of himself. [He texted that he wanted to apologize for being an embarrassment to his mother.]
He might have considered himself to be a 'piece of trash' from the head injury (injuries) and climbed into the dumpster to commit suicide.
Someone who is really messed up mentally might do anything.
Suicide is certainly not a rational thing to do...
However, that should not rule out foul play/murder.
The coroner should thoroughly investigate the scene to determine 'the facts'.