They made the joke of having first typoed the name of the company as "Twatter", before fixing it up to "Twitter". Visualizing a backspace in text as ^H is an old joke rooted in the backspace control character being ascii 08, which also maps to Ctrl-H.

The joke is intended to be funny because "twat" is a vulgar and generally derogatory term, and the author almost but not quite applied it to either a large company or (transitively) to its users.

I hope explaining the joke made it even funnier!

Possibly they’re implying they wanted to write Twatter but corrected it.

“Twat” is a mild to medium insult (idiot, asshole etc depending on tone)