Even with Musk's antics I don't see what would they gain by blocking API clients without announcing it - it would take Musk 30 seconds to tweet "oh btw third-party clients are done for" and would at least give everyone clarity.
But to play devils advocate, say you are thinking of removing third party apps. You want to test the waters and see if users who use them continue to visit at the same rate when forced to use the official client. You schedule a quite "blocking" of the apps for the evening PT, your team can happily sleep through the noise generated and have the data in the morning from Asia/Europe of how people reacted.
In the morning you make the call as to whether to stick with the plan or say it was an errant moderation bot.
That may be to much 4d chess though...
This is not an "API Outage", I think we can be 99.9% sure it's a removal of specific apps.