Some googling suggests this is what Dropbox does when it doesn’t like the owner or permissions of any files in the Dropbox folder. It is very weird though. I assume you have dropbox installed? It is syncing correctly? Running find /home/dullbananas/Dropbox/ ! -user 'dullbananas' will list any files in that folder that aren’t owned by you.

Assuming your userid is 1000 (likely but not guaranteed), running the script should be harmless and stop the password prompt from appearing until there is another file permission issue. Check your user id with id -u 'dullbananas'.

Surely the space is part of the command. It’s running sh with the file in /tmp as the parameter (run this file).