MU3001A
Based on the available and unless /until other info comes to the fore, I tend to agree with your sentiment in your final sentence. What I said re Customs however, I believe ditto Immigration. They process arrivals at the Port of Entry after landing. If the Pilot diverts the flight (rightly or wrongly) then they have an additional arrival to control. Unless the arrival was at an unapproved airstrip (obviously not) then they are presumably able to accommodate the odd diversion within operating hours. Arrivals are delayed all the time so are out of sequence anyway. I just found it odd that any of those agencies might 'speak sternly' even in these circs.