I have to admit to that one baffling me as well Bazile, as it's a look ive seen on quite a few Asian men (usually older ones) where I live.
Whilst we're on the topic, im also baffled why they still where the 2 piece outfits they wear. I (wrongly?) assumed that the original use for such outfits were to stay cool as well as modestly dressed in a hot climate, surely not applicable in a freezing winter here in the UK!
Still, what a ruddy kerfuffle eh? Can understand the 'need' for modesty, but the rules and regulations regarding everything else involving just their clothing is plain daft.
In Islam men should be covered from tummy (belly button) to below the knees (knees covered). And that is minimum requirement. Trouser could be anywhere between knees and ankles for modesty reasons. But it is not compulsory but is supposed to be better.
A friend opted to use his driver for the short hop from his home to the British Embassy for a do at which he was intending to wear a kilt to avoid causing offence and creating consternation whilst residing in Kabul.