Well yeah, you're not going to take a train to the corner store. Your PDF notes that 29% of trips are made on foot.

2% of trips by train is a lot higher than the number of trips by airplane... And again, 8% of people using trains once a week is a lot higher than they use planes...

...And yet I don't think anybody "grossly overestimates" the social and economic importance of airplanes.

People use trains to visit family, go sightseeing, and so forth. They're a hugely important part of infrastructure, even if most people don't use them daily.

If walking down to the corner shop is considered a "journey" then 2% of all journeys being made by train is a massive number.

Now try closing the railways of south-east England and see how well the roads hold up without them.