When you create an event and add an participant there is the option to not send an invitation to the particpant. Thus the person doesn't know you created an event with that person.
Steps to reproduce:
1. Create an event.
2. Add an participant.
3. Switch "send invitation" off.
No message for the participant. No entry in the calendar.
Why is that even possible? there is no reason to have a meeting without the person with that you're having the meeting knowing there is a meeting. We would like to remove that possibility and always send an invitation when adding participants. In order not to confuse it would be necessary to change the lable of the button "add participant" to "Invite participant" - otherwise people might not understand that an email will be send.