I presume he means as he described. That is, everything important that happens obviously occurs for the sake of the plot - things that are obviously the logical or natural course don't occur because the plot dictates that an illogical alternative has to take place.
One aspect of this regards the way characters act in a given situation. When you're considering what should or should not happen in a given scene, try to put yourself in your character's shoes, naturally considering the character you're trying to create (trying to temporarily "be", as such) in the process, and then decide if what the character should be thinking in that situation works with the way you're trying to advance the plot. If you can't get the current scene to fit in with the way the character should act, you're probably better off scrapping that scene entirely, or at least entirely rethinking it. I suggest you avoid trying to do this the other way around (that is, keeping the plot segment the same and moulding the character to it) as that'll throw everything that you've already done off.
Of course, that won't help you get to the root of the issue, but you'll be able to fix that by applying your brain whist writing.