What he means is that you aren't permitted to buzz in on Jeopardy until the host has completed reading the question and the buzzers are activated. Perhaps Watson is spamming the 'answer' button from the moment he knows the answer, or perhaps they let him cheat by sending him a signal when the buzzers become activated. Given that the process of buzzing in to answer a question is a large part of the strategy of the show though, I hope they aren't letting him cheat in that way.

Edit: Failed to read the comments lower on the page. Looks like Watson plays by the same rules as everyone else, using a physical buzzer which can't be activated until the question is read and the 'answer now' signal light is activated. I know that another restriction on when to answer that Watson has is that he won't buzz in until he's confident in an answer, while human players will sometimes buzz in figuring they will be able to come up with the answer in the couple seconds between buzzing and answering.

I don't think that's relevant. No one expected Deep Blue to have a mechanical arm that reaches out and moves pieces around a physical chess board.