DAMN sometimes I am dense---genset hookup

And to the OP, your inlet appears to be a NEMA L14-20, which as you stated is two hots and a neutral. That said, if the overcurrent protection device on your generator is higher than 20 amps, I would recommend you upgrade the inlet receptacle and associated wiring to match the generator output, especially considering it appears to be feeding a 50 amp breaker. If the generator OCPD is greater than 20 amps your inlet and wiring (assuming 12ga) is not adequately protected.