Some features had a bug which lead to uninitialized memory (AKA previous memory contents) in the output of a malformed HTML page was requested.
As one such server handles many sites, everything that the server handled before that request may be compromised. This includes all HTTP-GET/POST data (credentials, direct messages to other users, ...), Headers (API tokens, Login-Cookies) and contents.
So, you have to assume that everything you did on a CF "protected" website in the last months (especially between 2017-02-13 and 2017-02-17) is potentially compromised.
It's C. If you have an array, you may only compare to one element behind the last. Everything else is undefined behavior. So a compiler may just "optimize" your >= to ==.