@noiob no.

a cuppa is always tea.

if you wanted coffee you'd ask for a coffee.

this is only mostly joking btw lmao. we literally use 'cuppa' as a synonym for 'cup or other suitable receptacle of tea', same as 'pop the kettle on' means 'make a cup of tea please'. At no point does coffee even enter the discussion or thought process for either of these, even though by rights it should in the second example.

I don't think it's done consciously either. We just assume "cuppa" = tea. and nobody asks for a "cuppa coffee". hell it even sounds fucking wrong to say it, even though "cuppa" is a truncated, shortened form of "cup of", and we would literally ask for a "cup of coffee" if we wanted one. or "a coffee", missing the cup part, more likely.