Oracles lawyers and Githubs lawyers then disagree cause Githubs CEO stated the same thing as the GP: They block people based on location, not on nationality. If you are banned but not in one of the banned locations you can fill out a form to get unblocked:

https://twitter.com/natfriedman/status/1155311123467399168

Of course this is one of the intended consequences of any capricious military-state outrage. Uncertainty allows them to oppress more people while simultaneously claiming that wasn't their intent. The firms who are applying a broad brush are doing exactly what the armaments lobbyists desire.

IANAL but it seems to me like Oracle's lawyers have taken a stronger position than required by law.

Nationality of individuals is primarily relevant for deemed-export under ITAR/EAR; not the OFAC sanctions on Iran.