At present, as far as I know, the flight attendants on high-speed rail and EMU are divided into career establishment and labor dispatch system. Take tianjin railway station East Railway Station as an example: many young ticket inspectors or customer service personnel wearing red trench coats or uniforms in the station, as well as all the cleaning service personnel wearing purple clothes in each carriage of such trains, are all labor dispatch, that is, they are sent to work in the railway station through cooperation with dispatching companies. However, their labor relationship is not established with the railway station, but with the labor dispatch company. That is to say, these people actually belong to the employees of the dispatch company and just work in the railway station.
So the recruitment information you said is true, but whether the labor dispatch company you said has a labor cooperation relationship with a high-speed railway station and whether the post that can be stationed is a flight attendant needs to refer to the specific contents of the labor contract they concluded with the railway station.
I haven't been in contact with the dispatching company you mentioned, so I can't intuitively judge the authenticity of the information he provided. I only use the above contents as reference suggestions, hoping to help you!