I wonder if they had weapons? Federal officials(FBI,ATF.....) often board airplanes with their duty weapon. If they had weapons, this aint no dry run. Air marshalls typically board planes prior to passengers, introduce themselves to the crew and make sure all is comfortable.
Should you be posting that tidbit of info on the internet? It may not be top secret, yet it is not common knowledge, and might be useful to some bad people.
All Federal law enforcement officers must be in compliance with 14 CFR Part 108 of the Federal Aviation Regulations. These governing regulations place certain restrictions on both airlines and federal law enforcement officials. Under these regulations, law enforcement officers in official travel status who are required to report armed and immediately ready for duty are permitted to travel armed (weapon in their immediate control) on board a commercial aircraft. These are additional qualifying conditions for flying armed, including: agency firearms authorization based upon arrest authority, completion of a certified training course covering Federal Aviation Administration (FAA) guidelines and alcohol abstinence. Additionally, you must present proper credentials and complete required airline forms.