30 amp shore power provides only enough electrical power to run one ac, and the manual switch selects which a/c is powered from the primary, shore power circuit. Your generator is wired to power both a/cs, one receiving power via the primary circuit (same one as is powered from shore power) and one via a separate circuit direct from the generator. Regardless of the switch position, both a/c's should work on the generator.
The transfer switch changes between shore and generator power and always selects the generator if it is running and putting out power. This switch is located at the point where the shore power and generator wiring come together, usually where the shore cord is connected. If the circuit breaker on the genset is tripped, the transfer switch will never see power from the genset. It switches only the primary power circuit, i.e. the 30A power from either shore or generator.
There is a separate circuit for the second a/c power from the genset and it should have its own circuit breaker. It does not go through the transfer switch. My guess is that this independent circuit breaker has tripped. Hard to say where it might be located, though.
