Most PSD templates for screenshots are Macbook screens + Safari. Having designed a number of landing pages for startups I'm really not surprised that the designer they hired for their website chose to use that (without considering the current browser support).

As the other commenter pointed out it's a safe bet for marketing purposes and looks best aesthetically. But the confusion here could be a real problem for early adopters.

Designer here. This is accurate. The long story is, this site was mocked a bit before all the final technical details were scoped out for the project. It's in need of a visual refresh to more accurately represent the platforms we use.