It can be both. An AMA is "Ask me anything" which is more focused on somebody (Or something that happened).. which is very different than the same person posting a meaningful comment on a discussion. As far as I know, PG regularly comments on HN and there are often links to his essay or interviews. An AMA isn't so much different than an interview...
The implication is that HNers are more interested in Q&A sessions over what amounts to a lecture. You could frame that as positively or negatively as you like: a fixation on fame and fortune over substance; a disinterest in having someone else explain what you could learn on your own; a preference for an interactive setting rather than a receptive one; etc.