I'm not defending Twitter or their policy in any way (disclaimer: I left Twitter the moment Elmo took over. I despise his hypocrisy and his fascist ideas) But this could be a "legitimate f-up". Normally, most of these unsafe-url protection and detection is automated in something with the scale of Twitter. Just like URL-shorteners often are (were?) "seemingly randomly" banned, because a portion of the shared urls are…
The purpose of a system is what it does.
This is only true for systems that works perfectly. If the implementation if flawed, the system can do something different from its purpose.
Claiming "The purpose of a system is what it does." is like claiming that software bugs do not exist.