"A coworker prank where the error text was directly typed into the Result Messages tab"
What? Can't do.
you can write some text there, but not in red. The "correct" explicitly says "error text", which is in red.
The correct answer would be a trojan, which reformats drive C, returns message and then passes the request to original sqlserver, which in turn returns the error message, because drive C is unexpectedly empty.
Can't format a drive in use? Right, the format command won't do it, but there are still ways to do it.
A trojan itself could be just a prank and just return the error message without doing any damage, but type the error text in red directly into message windows, nak.