The web site states, as a matter of fact, that all engineering problems to colonize Mars must be first solved on the moon. That's not really a fact, though, is it? Like, it seems like a reasonable plan for incrementally derisking things, but it doesn't seem strictly necessary.

It also seems like there's technical problems that are unique to Mars, and technical problems that are unique to the moon. For example, landing on the moon can only really be done propulsively due to the lack of atmosphere. On Mars, though, there's atmosphere to aero-brake with. Or, insulation is relatively easy on the moon because of the lack of convection and conduction, while it's really difficult on Mars despite the temperature swings being considerably less severe.