Unlike DC voltage you can’t easily series AC power due to the phasing of the alternating current. The Honda’s are designed to sync their phases, but they have to be connected in parallel for that to work.
Household 240V is in fact 2 120V legs, but the are phases 180° apart. Even thou it has 2 hot wires it is still called single phase. If you think about overhead power lines single phase is one wire (plus ground) and three phase is 3 wires (plus ground). The transformer then takes that single phase, often 7200V or higher, and transforms it down to 120V on two legs with 180° of phase separation, which is household 240V single phase power.
If it’s a 4 wire 240V plug there is a neutral so that the appliance can also use 120V.