This is easy to debunk. Austria is part of EU grid, and other states produce big part of their electricity from coal and gas. Austria imports that electricity!
Plus some trains operated by Oebb are international!
So according to the company’s 2022 annual report, they source power from 8 hydroelectric and 6 solar power plants, all of which they operate themselves, as well as 4 partnering hydroelectric plants. The rest of their electricity needs is acquired from the market but checked for proof of origin.
Obviously this only covers railway infrastructure in Austria as they have no influence over other countries.
Source in German: https://presse.oebb.at/dam/jcr:f87d6627-602c-47d6-bec7-f5682...
"Each day, our trains pull x MWh of energy from the grid and we're paying renewable energy providers for y >= x MWh - therefore we can say our trains run on 100% renewable power."
Whether or not some of the electron domino that finds its end in a train's motor coils happen to have started in a coal plant doesn't matter for this calculation.
You can like this or not, but I guess there aren't a lot of better options as long as renewable and fossil power sources are both supplying the same grid and energy is effectively fungible.