This article is a load of bullshit. They basically only compared train prices from the UK to Europe and said it was more than flying. Sure, but that's because train prices in the UK are ridiculous, not because train prices in Europe are ridiculous. The UK is the outlier, always has been.
Taking a train in the UK, even across the UK, is sometimes more expensive than driving - it usually is when you factor in getting from a station to somewhere else. Meanwhile, taking a train within Europe is generally very affordable. The difference is the governments in the mainland actually regulate and ensure investment.
In Germany you can get a train to anywhere in the country for about €20, and children up to 14 are free. There's also Interrail tickets you can get across Europe that cover regions or countries, when the UK was a part of this system the UK-wide ticket cost roughly the price of 3 EU countries, even though the UK is much smaller.