gent silence and sound alarm events in an empty building

hello,
     one of our guys had a gent vigilon record in the event log several 'alarms silenced' and 'alarms sounded' events on saturday night in an unoccupied office building (so no-one was pressing the panel buttons). Can these 'alarms silenced' and 'alarms sounded' events only occur from the silence and sound buttons from the panel or can, for instance, they come in from another interface or device set up by some weird programming to operate the panel sound and silence buttons?

p.s. this was an old gent 3400 panel recently upgraded to a vigilon running old software to run existing old devices. 'new' panel has already been changed once due to problems...