Michael O'Leary 's motive in spreading the word like that is to engineer a loss of confidence resulting in people not paying for bookings with the airlines concerned, thus damaging the cash flow of the airlines concerned, and triggering a rapid slide into bankruptcy.
It's a deliberate, classic and very effective tactic, so long as it does not backfire.
Which it won't; Ryanair has huge reserves, augmented by the large financial benefit derived from Boeing's problems.