In a way, I do understand why they would phrase it this way. 'No deal' sounds like you're heading into the great unknown, 'Australia-type deal' sounds like you're getting into a known situation. And it's true in that sense: the EU wouldn't be the only place on earth with which the UK has to trade on WHO terms, so it's not like everyone is completely in the dark as to what a 'no deal' situation means. I think it makes sense that a government would want to build that aspect into its messaging.
But yeah, of course, the way it's being done now also suggests that everything is fine and under control, completely downplaying the huge economic disadvantages of a no-deal situation, the enormous change it situation would bring about, and the UK's level of unpreparedness for that change. There's spin and then there's full-on bullshitting.
I really think that it's a narrative built around the CANZUK idea, it's not much about the fact that "No deal" sounds terrible but that they are actively targeting a certain demographic and selling the dream of an Anglosphere led by the UK.