As far as I know the term "governmental" entity has not been clearly defined by the IRS or in ERISA. The IRS issued proposed regulations, and this was supposedly going to be coordinated with IRS, DOL, and PBGC so there would be consistency, but I'm not aware that they have been finalized.
If you have access to the EOB, Sal has a great discussion of this. In the meantime, this might help.
https://www.federalregister.gov/documents/2011/11/08/2011-28853/determination-of-governmental-plan-status