As I vaguely understand it, and I’m not an expert at all here - American 220V is two 110V phases tapped off the feed and glued together at 180 degree offsets; European 240V is one phase tapped directly off the mains feed. So it’s definitely constructed differently! Their battery could tap into the electric range 220V/50A circuit and then redistributing that somehow - or it could tap into the 110V 15A circuit and synthesize 220V/xxA itself. I’m not sure what makes the most sense, or how the NEMA outlet legalities work out! But it’s definitely a lot of interesting research.
That should mean there are UPSs already available, although possibly they don't come in small sizes.