The most important part of the code is understanding when an article applies.
We are talking about PORTABLE generators not premises wiring.
250.20(B) Alternating-Current Systems of 50 Volts to 1000 Volts. Alternating-current systems of 50 volts to 1000 volts that supply premises wiring and premises wiring systems shall be grounded
NOPE
250.26 Conductor to Be Grounded — Alternating-Current Systems.
For ac premises wiring systems, the conductor to be grounded shall be as specified in the following...
NOPE
250.34(C) Grounded Conductor Bonding. A system conductor that is required to be grounded by 250.26...
NOPE
All of these refer to "premises" wiring.
When you connect a generator to a building it does require grounding the neutral but if you simply switch the phases with the transfer equipment and bring the neutral and ground straight in you use the system main bonding jumper to accomplish that.
In fact if you use a transfer switch like that you create a violation if you do have the generator grounding the neutral.
