Should have briefed him?
How many pilots do you know?
I've know plenty and none would have let a non-pilot in their plane without some form of pre-flight instruction about what to do or not do.

And from the article:
"The spokesman said the flight had been cleared and all procedures adhered to "prior to the passenger boarding the aircraft", making it unlikely charges would follow. [...]

Passengers would have been briefed on the ejection sequence and warned that the "loop" between his legs was not to be touched unless the pilot called "Eject, eject, eject" during the flight. Such a briefing is done routinely, even when two qualified pilots are involved in the flight. It is likely the rear cockpit was extensively damaged by the firing of the cartridges and rockets during the ejection."

I bet you a nickel he was stupidly holding the thing out of fear and when the plane lurched ~ ~ ~ ~ ~ ~ ~ ~ ~