Those promises are "easy" to achieve for a certain interpretation of what they mean.

BASIC itself, through things like peek and poke, can give you the "power of C", and with subroutines if you create a stdlib that you inject, you can certainly make it as high-level and versatile as Python.

That doesn't mean that you get the benefits of C, Python and BASIC all at once though. You've achieved the overly-broad goals, and can say you haven't lied, but the impression the consumer has won't live up to the real world - because they're expecting the cultures and communities of those languages as well.