You suggested I "didn't get it" because trolling stuff that wins a game was the point. Actually, what made me think about impact was on website and the challenge itself:

"Backdoor Insertion Proof-of-Concept Bounty: The first time someone tricks me into inserting the string "BackdoorPoCTwitter" into a release of any of my software projects"

Whole point is assessing ability to backdoor software products. Social attack that succeeds might teach us something. The cheat teaches us nothing but is amusing. So, I certainly get it and read site before I wrote here. ;)

Note: Same page said employer's website was off limits in hacks and pentests. I assumed that meant Defuse. So, never considered website attack as in scope in first place.

The attacker thought out of the box to tackle a lesser challenge: getting a string on the website itself. It was technically true under rules, funny, and contest issuer even owned up to it. It's not the real challenge, though. No real-world impact. So, just amusing trolling.