I would be skeptical, but I trust the BBC.
From the books I have read about the war in Syria, the Coalition is a disaster. It's a loose collection of militias and private armies with varying degrees or training, equipment and motivation. Most army owners don't want to use up their guys in fighting something as serious as ISIS. They would rather keep them intact for looting and turf wars after ISIS is kicked out. So the US bombs ISIS out of a stronghold and then cajoles and bribes the Coalition ground troops to make a final push to actually take the ground. ISIS boobytraps everything and so none of the coalition guys are anxious for the clear out job.
Afterwards, everybody who is important gets a photo op, a medal and a promotion.
The most effective coalition guys are the Peshmerga - who can and do kick ass - and the Shiite militias who are basically the property of Iran.
It could be a consideration that ISIS has nowhere to go after Raqqa falls and this essentially ends the war quickly.
The estimate is that 1 in 9 foreign fighters remains active after leaving the war zone. Many apparently drift back into civilian lives and leave ISIS behind. Some of course will remain major problems in the future.
