Talking about a soccer team: "Belgium is" or "Belgium are"?

The short answer to your question about the sentence above is that this sentence is from TheGuardian.com, a British news site.

To explain further, in British English, a collective noun, or a noun that refers to a group of people, like team, government, or company, can be used with either a singular or a plural verb.

For example, both of these sentences would be considered correct by most British English speakers:  

1. The Belgian team has made it to the second round. (has is a singular verb)
2. The Belgian team have made it to the second round. (have is a plural verb)

and version 2 is probably more typical. In American English, however, nearly all collective nouns are used with singular verbs only, so version 2 sounds completely wrong to an American.  

In your sentence, which is about the results of a World Cup soccer match (“Belgium are through to the second round after Eden Hazard inspired them to a 1-0 win over Russia”), Belgium is shorthand for the soccer team of Belgium, a collective noun. Therefore the use of are with Belgium is not surprising.

I hope this is helpful.