It always pays off to do one's homework before booking a flight ticket but this is especially true when traveling with a bike as policies and charges vary significantly from one airline to another.

I suspect that the page is clumsily phrased and that the dimensions are those of the box that KL offers rather than max dimensions. Since you will need to phone KL at least 48 hours before the flight to "book" space for your bike and will need to provide dimensions at this point, it won't be a case of "just turn up and hope for the best". If you have booked your ticket already, there is no reason not to phone and book the space right now. Arm yourself with patience and forbearance, however, as I would not be surprised if the agent you speak to is not particularly well-informed. Unless they have done it before, the odds of the agent not really knowing what to do are fairly high as I doubt that special baggage handling procedures are part of the standard training for customer service agents.