Since you asked - the going rate for an RB211 overhaul is around the $5 million mark. RB211s do occasionally smoke after shutdown (but only outside a public building .. I'll get me coat) and I've never heard of anyone reacting to this with anything more than a polite enquiry before.
I think Super VC10 may well have hit the nail on the head with the ATC message - but I wasn't there so that's pure conjecture.