In my opinion, "that board will ride you" would just mean, it will be tough for you to control. This would simply just be with respect to a board too long and too stiff for a newb. But as the rest of this thread has clearly pointed out, in the end it doesn't really matter now does it? All these people with examples of broken, ill-fitting boards as their first, yet they are still here. If you go out and fall in love with riding, but get the wrong board as your first, it doesn't matter. You will still go out and ride your ass off and eventually beat up your board enough to buy a new one.
Outside of that scenario, anyone that says, "that board will ride you" to a newb that bought a board that is too "advanced" (aka expensive) for that newb's skill level, is just jelly that the newb can afford a shinier stick than they can.