A lot of people who are not from Britain, usually say 'England' to refer to Britain. Dutch people do this all the time. I usually respond with "Only in England, or also in Scotland and Wales (and Northern Ireland)?" Most people react confused.
It is very easy to understand the different terms.

Great Britain (island) is England, Wales and Scotland.
The United Kingdom (sovereign state) is Great Britain plus Northern Ireland. The abbreviation 'Britain' is used to refer to both the island and the state. Not complicated at all.

I wonder what people from Britain think when they hear foreigners say 'England' instead of Britain.