All Dr. Tanenbaum is saying is that it would have been the classy thing to let him know, nothing more. Professor Tanenbaum is one of the most respected computer scientists alive, and for Intel to include Minix in their chip and not let him know is kind of unprofessional and not very nice to say the least. That is his only (and quite fair) point.
Nope. His letter point is clearly about widely(1) known debate(2) between him and Linus Torvalds, and ego massage. (1) widely, if you arent 25 years old proverbial "javascript developer" ;-) - as the debate took place in 1992. (2) https://en.wikipedia.org/wiki/Tanenbaum%E2%80%93Torvalds_deb...
I think the reason he posts this is that, just like everybody else, he's not happy about Intel secretly introducing a massive security hole in their processors. Telling him they were using Minix on such a massive scale would have been polite, but it would also have informed Tanenbaum that Intel was running a secret OS on their processors.
What Intel did was not only foolish and harmful, it was also impolite. Plenty of people are addressing the foolish and harmful parts already, but the impolite part can only really be addressed by AST.