Two possibilities:

1) He had savings he didn't tell them about that took him above the threshold for qualifying for claiming which they subsequently found during an investigation. £16,000 or more and you're not entitled to claim. Between £10,000 and £16,000 they taper off your claim, below £10,000 you get the full amount.

2) Or he didn't tell them he'd voluntarily left his employment. They then cancelled his claim, as voluntarily leaving results in a sanction, and he had to repay all he had been paid out from all of the benefits because it is a knock on as he would have declared he was on JSA for council tax benefit and mortgage interest help.