since he made it public already then this is close to just promotion of the bull run cycle. he been doing this since the time he appeared to the public for Bitcoin. maybe another announcement will be made when the bear market starts. he could start by saying 'i was only joking'.
I also believe that it is nothing but PR, if he has truly taken this kind of decision, i doubt he will make it public, he would simply make it impossible for anyone to find his seed phrase when he is gone. I don't believe most things people say on the internet, there is usually a hidden motive to what they say.
Yes, must of the things people say or do on the internet is just creating personal publicity and drawing additional followers for themselves especially on social networks like Twitter and Facebook.
I am very skeptic about pronouncement on social networks about people's gestures, many of them are just people seeking attentions and trying to be relevant.
Like you mentioned, if truly Micheal Saylor want to give his Bitcoin to humanity, it shouldn't make it a public hearing, It should have been kept out of public notice until when he is old and plans to retire from active service. This is my opinion.