X is not mentioned in the title and the very first sentence of the article says that the BBC accounts are still on X/Twitter. What gives you the impression that the intention was for this to be read as the contrary?
Twitter/X is the 'default' and the assumption that media will be on it...while Threads and Mastodon are the _alternatives_. This article, to me, is just suggesting that BBC has dropped _one of the alternatives_.
Less of the bumptious tone please.
Threads and Mastodon are both _alternative_ choices, with Twitter being the main real-time shortform source. TFA highlights that BBC is giving up on threads, but not on alternatives in general.