How many places have you visited? For example just the small nation of the Czech Republic is very different every 100 kilometers. People in Prague almost universally understand English and very probably use it daily because it's very common to have foreign friends (that reside in Prague); if you attend university, some classes are taught in English and many of your colleagues are foreign. I work in a company that has 150+ people out of which 10 are Czech. People in Moravia do not generally speak English so well. People in Brno sometimes do. The younger generations all around the republic (that attended primary schools after the Velvet Revolution) generally understand English very well and can have a conversation about work as well as about other topics.

It's 51% including the UK and Ireland. Also included are places like Norway, The Netherlands and Denmark. So even if in 2/3rds of the countries having a fluent conversation in English is hard or impossible with most inhabitants still the majority of the people that live in Europe speak it well enough.

I think even less people speak Spanish in the US while about 1/3rd of the country used to be Spanish and the rest of the continent bar Canada speaks it.

The vast majority of people who live in Europe are not able to hold a conversation in English.

Your 51% counts any people who attended an English class in school. It's not a meaningful level of proficiency.