This article makes no effort to see if the bug is also replicated on tweets by non-left or non political. There is scant evidence to support the idea that this is more than a bug. If a hard to fix bug is going to occur, of course you can expect that it might appear on tweets with many replies. Is there something more I am missing?
Maybe a coder at Twitter inverted a sign somewhere.
The fact that censoring the left is shocking, but censoring the right is heroic tells us everything we need to know about the world in 2019. It is also exactly why people vote for Trump, Johnson, Bolsonaro, etc., etc...