NodeBB core doesn't have anything to prevent this. But plugins can be made to prevent multiple accounts from the same IP etc although it can be easily by passed.
Why "Moderator" can't Edit Topic of Others?
This is one of the issue I am facing, where I created a group called "Moderator" and we are not able to give any special permission to them like, editing the topic or deleting it.
In this case; the "Moderator" reverted back and asked "What special permission does he has other than general users?"
Any help on this?
Got the solution.
The option is available under Manage > Categories > Options > Access Control > Search User > Privileges.