When the Create Issue Permission granted to "User Custom Field" or "Reporter" or "Group Custom Field Value".
This mean the Create Issue had been granted to ANYONE.

Use Case:-
When A project permission scheme of Create Issue is ONLY granted to "User Custom Field Value"

Where the custom have no default or predefined User selected

Result:-
ANYONE can create issue which is not expected

Suggestion:
Disable or warn user when User choose Reporter or "User Custom Field" or "Group Custom Field Value" that this indicates Anyone