This is just my personal guess, but it's likely China flexing again after the protest escalation yesterday in Hong Kong. A few weeks ago Telegram was attacked by China [0], and Hong Kong protesters used Telegram to communicate.

This time when CloudFlare was down, the most popular local forum among protesters, lihkg.com, was brought down as well.

[0]: https://techcrunch.com/2019/06/12/telegram-faces-ddos-attack...