What happened in those 10 minutes is not entirely clear, but initial reports claim the man was “acting really crazy” and had some wires and batteries in his bag. I’ll go out on a limb here and assume the guy was indeed crazy, and had something in his bag that looked like bomb parts.
As soon as the “bomb” was detected, the evacuation started.
Flights heading to LaGuardia were diverted, and as of right now (9:30am), the airport is still under a ground stop, though passengers are being allowed back into the terminal buildings.
Many flights in and out of the airport are delayed by up to 3 hours, so if you are heading to LGA today, keep an eye on any announcements or flight status notifications from your airline.