Another wikipedia article states this, which I based my assumption to.

>Mild climate and trade winds make neither heating nor cooling necessary, particularly in the highland cities and towns where some 90% of the population lives.

https://en.wikipedia.org/wiki/Economy_of_Costa_Rica

And here's a final wikipedia article that probably explains why he corrected you

https://en.wikipedia.org/wiki/Temperate_climate

Fair enough should probably have used the mild climate term used in the wikipedia article to avoid confusing to climate zones.

In the capital San Jose it has about a mile's altitude and is in a valley ringed by mountains. In the capital every day is pretty much 70 - 80s F / 20s C and a little colder in the mountains, the coastlines are at sea level and quite hot.

>the coastlines are at sea level

You don't say!

At least in the political/socioeconomic sense (though perhaps not in the literal sense of "the point where water meets land"), lots of what we consider to be a "coastline" is actually well above sea level (for example: sea cliffs).