Update: some press coverage raising the same questions. The silly part about this is the filing deficiencies seem either inept or willful. Mr. Musk can certainly afford good securities lawyers to make the proper filings. A 13D is not that much more burdensome than a 13G, and some activists use the filing (which gets a lot of free attention) to make statements that to support their objective, whatever that may be.

https://www.wsj.com/articles/elon-musks-twitter-investment-r...

Second update: the inevitable Matt Levine column on the same theme: https://www.bloomberglaw.com/bloomberglawnews/mergers-and-ac...