See minute 53:30 in https://www.youtube.com/watch?v=TRrL5j3MIvo&feature=youtu.be

If you open the dev tools and look in the NETWORK tab you'll see "Failed to load resource", when page loads before the json data has loaded it evaluates the templates, at which point countryFlag.URL template becomes what it's trying to fetch What you need to to to avoid it, use ng-src only sends the source after the moulde has been loaded (after the template has been evaluated see example 28 in video)

Country	Population	Flag
{{country.name}}	{{country.population}}