So to be clear, the article isn't suggesting that e.g. github will interpret the ANSI escape sequences, but they will be when you `git log` from a command line, right?
We cannot know (in principle) what GitHub does with data streams sent their way, but in the case of the blinking, the target is your terminal. It will interpret and “execute” (by modifying display) any text it is given.
[1] https://en.wikipedia.org/wiki/ANSI_escape_code