How exactly would an Afghan not be a credible refugee? There is still a war going on there and suicide bombings occur almost daily.
That's not enough to be considered a refugee.
A refugee is:
"A person who owing to a well-founded fear of being persecuted for reasons of race, religion, nationality, membership of a particular social group or political opinion, is outside the country of his nationality and is unable or, owing to such fear, is unwilling to avail himself of the protection of that country; or who, not having a nationality and being outside the country of his former habitual residence as a result of such events, is unable or, owing to such fear, is unwilling to return to it.."
Also, whilst there is subsidiary protection in Belgium (
https://en.wikipedia.org/wiki/Subsidiary_protection), some parts of Afghanistan are generally considered safe. Some asylum seekers will therefore either lie about being persecuted or lie about where in Afghanistan they're from.
But honestly I can deal with that type of lies. It's normal for people to want to improve their lives and I can understand them when they say they don't want to go back to Afghanistan. The problem is a lot of these Afghans seem to have had no education or decent upbringing whatsoever. Add to that the fact the vast majority are young men and I'm sure you realise in what way they might cause significant problems for other (female) refugees.