You see this with healthcare in different places: Details change and sometimes it is lacking, but lots of places offer healthcare to its citizens that is low-cost to free when you need it. There is a lot of variation in what countries can do. Some places are poor but still manage to a point. Some places just refuse, like the US - heck, the US has oil and could have funded things for its citizens and keeps bragging about being rich, but they aren't gonna use it for the immediate welfare of its citizens.
that doesn't make any sense for two reasons. first, he only entered the EU in september this year, so either the 90 days are not up yet or he should be in mexico now. is he? but why would he fly to mexico when he could just go to the UK?
but more importantly, he is a british citizen. getting a visa to walk through europe, especially now that he already has a track record of walking for so long should really not be an issue.
I live in Norway, have residence and stuff. I can travel freely through most of europe without much hassle - but I can only travel 90 days out of 180 days - then you gotta go out of the area (or back to your home country if it is inside), stay out or home for 90 days, and then start anew. The closest border to me - one to Sweden - has no real security. A customs office because there is border shopping in the area and I know they very occasionally stop folks. A crossing an slightly inconvenient distance north just has signs.
Anything outside of this requires paperwork.