Difference can be seen from definitions:
" An unplanned interruption to an IT service or reduction in the quality of an IT service."
" A change of state that has significance for the management of an IT service or other configuration item. "
Meaning, in case of event - everything is OK, still didn't happen some kind of error in the service. Something just changed, e.g. mail arrived at destination, batch job completed, door opened. Further on, event can detect malfunctioning, e.g. port on the router is down. Then it triggers incident. So, event can be used for information or to trigger incidents.