It's important to note that Twitter's desires are fundamentally at odds with the desires of the content creators on Twitter on this point. Twitter, ideally, wants to only show it's tweet to real people who will click on an ad, since it costs money to show tweets and bots or people who don't look at ads are not paying that money back. Creators on Twitter want their tweet to be shown to anyone at all, and will leave if they feel people just aren't seeing their tweets.
So, Twitter must walk a fine line when trying to restrict who can see their tweets, lest they alienate content creators. Inventing a common foe is a tried-and-true tactic for getting people to accept changes that hurt them.
1. Twitter decides to go account only for monetization reasons, and implements this feature with some bugs.
2. People start complaining about the new Twitter policy.
3. Availability issues start being observed, caused by the bugs in the implementation of 1 - possibly a self-DDoS.
4. Elon, in response to 2, lies about 1 being a temporary response to an external pre-existing DDoS attack. People start associating 3 with the claimed DDoS attack.
5. In a hasty attempt to fix 3, whose exact cause they have not yet determined, Twitter starts implementing stringent view quotas. Since 3 was not caused by an external DDoS attack, this actually only makes the problem worse.
I'm not claiming this is definitely what happened, just that it is a plausible time-line of events. The one Elon presented is also plausible, of course.
The best question that could help us distinguish these two cases from the outside is whether Twitter's availability issues started being observed before or after the authentication policy change. I would say that Elon's claim is far less likely to be true if the noticeable availability issues only appeared after the policy change. Conversely, my version of events (which is more or less the same as TFA's, I think) is far less believable if the availability issues happened before the Auth change.
I will note that I didn't use Twitter at all in the last few days and thus don't know which is the case. On HN, I definitely saw the Auth policy change story at least a day before seeing significant complaints about other availability issues, though.