I can't be the only person trying to figure out why inbounds were being cleared to land after the initial report of a cowling on the runway...
Considering that a cowling doesn't just fall off without a reason, there easily could have been more debris scattered across the runway, which may have separated earlier - like on touch down or when thrust reversers were deployed. Such smaller stuff is invisible from a longer distance. So I also find it a bit strange that they just cleared other aircraft.
Btw, the Concorde crash in 2000 was triggered by a small part from an engine cowling lying on the runway - and was also lost by a DC-10. Though, the part they lost at the time was an unapproved and improperly installed patch - so that wasn't really a DC-10 specific issue. Still, a reason to be careful with debris.