canadiancow

The context around that number is a three-cabin, F/J/Y configuration of the style most airlines were installing at the time. 8 F, 40+ J, 9-across Y, etc.

It was never meant as "this is what we think is good/safe/etc." It was "this is what our customers want". Yes, the aircraft was designed for the cabin configuration requested by the prospective purchasers.

In fact, on the page you linked, all it says is how far it can carry 365 passengers. It doesn't mention anything about capacity or "designed for".