From that same article:

"U.S. Customs and Border Protection is now checking luggage for drugs and cash, Fox 29's Dave Schratwieser reported Thursday afternoon from the airport."

A totally unfounded wild guess here, but I think the drug angle is actually plausible here-- the unknown person tosses a bag (not connected with any on-board passenger) filled with drugs, etc. onto the airplane, intended to be picked up by a co-hort at the destination. (though wouldn't it be more likely that it would be coming INTO the US rather than leaving?)

Brings up an interesting question - if they come across anything illegal in an onboard-passenger's bag during the search, how will the 'probable cause' issue come into play, since they're specifically stating they're looking for drugs/cash as opposed to a bomb, etc.?