Quite a common issue, the connectors under the seats seem a bit poor, or at least in mine they were. Would randomly come on, sometimes twice in a week, sometimes not for over a year
As suggested above, check the connectors under the seaet, and do the airbag reset and see if it gets triggered again. If it comes on again, get it sorted. Did you get the car from Nissan? If so just get them to look at it anyway