Sadly I think this sounds like the case, doesn't it. All the examples various players (Shapps, Khan, Burnham) come up with are ridiculous. The SoS was going on about eating a sandwich with a mask half off being silly (you can do this already), Johnson was saying something about if you were sat in an empty carriage at midnight for hours you could take it off, and the Mayors are insisting that every train is full of desperately ill and vulnerable people going to cancer appointments at all hours of the day. Then mixing up guidance with conditions of carriage, operators doing X but not Y, easyJet saying you must...it'll be 'interesting' to see what they come up with..!I think you have his position exactly right.
Shapps will be fully aware that making the 17:44 service mandatory but the 15:44 voluntary would be completely unworkable.
In reality, the government's position means that operators have been empowered to continue to require masks as a blanket restriction as this will be easier to manage operationally and allow them to appease the pressure to keep social distancing measures from unions and the likes of Andy Burnham etc, whilst ensuring that any backlash is deflected locally and not towards the Government.