'cause that would be irrelevant if the objective is to minimize the use of limited helium resources on earth.

Or so I thought, yet they seem to be concerned about the transportation cost and greenhouse gas emission of transporting helium containers to the station.

Baffled.

Probably natural gas: https://www.arm.gov/capabilities/observatories/nsa/locations...

I know people have filled balloons with hydrogen that they made by mixing an acid with a metal.

Unless they have a power purchase agreement then that would depend entirely on whatever the local grid mix is at the time. Bear in mind researchers aren't usually the ones running the physical facilities in big labs. There will be a whole ops department leading that, folks build a career on that.