I think I may have it figured out.
Since the information is in an RFP, we can't contact anyone in the City about technical questions until the project has been awarded. Also, the detailed design has not been done yet. What is presented in the RFP is the design concept.
I think the portable E/G may be easily connectable for either 480vac/3-ph or 240vac/3-phase. In this case a neutral may be brought out with three phase conductors. The neutral may be the center of one of the delta phases. It looks like the City's intent is to connect the generator windings in the 240v 3-ph configuration and use the phase with the center tap (neutral) as a 120/240v 3-wire 1-phase source.
If this is the case, will this arrangement work OK on a single phase 240v and 120v loads?