The node OnNotifyFromActor inherits the identity tag match type from the ObserveActor node, however in the function OnNotifyFromComponent it strictly calls HasAnyExact on the identity tags and doesn't use the match type.
void UFlowNode_OnNotifyFromActor::OnNotifyFromComponent(UFlowComponent* Component, const FGameplayTag& Tag)
{
if (Component->IdentityTags.HasAnyExact(IdentityTags) && (!NotifyTags.IsValid() || NotifyTags.HasTagExact(Tag)))
{
OnEventReceived();
}
}
This means any child tags will not be matched. In the attached screenshot for example, any child tag of Flow.Pawn.Collectible.Tombstone won't trigger the notify.