A “maisonette” is an apartment spreading over 2 floors, nothing more than that. A maisonette does not require a separate entrance as described in the wiki and a separate entrance into an upper floor flat does not make the flat it a maisonette either.
Having said that I have no idea what house=maisonette is standing for. An apartment spreading over 2 floors inside a residential building is not a “house” and tagging such an apartment as house=maisonette inside a building=apartments does not make any sense to me.
Btw: The sample pic on the wiki page of house=maisonette shows a “one-above-another” duplex house as described in the OP. This is something quite different from a maisonette apartement.