Internet jargon; when a commenter is overly excited, they tend to overuse exclamation points. In the rush to add many exclamation points, the shift key might not be held down for all of them.

So you end up with things like "OMG!!!!111"

It's probably a running joke internally---anecdotally, I've came across it a few times on different Google properties over the years.

Someone forgot to hold down thr shift key when typing the third mark?

Secret status code to differentiate types or server errors?

A joke?