Google Calendar can create events automatically when an email comes in, examples of this would be plane flights, hotel reservations or invitations from emails. If other people depend on viewing your calendar or assist you in managing yours, they may miss these events. It's an easy fix to resolve this:
First go to your Google settings by clicking the gear icon in the upper right:
Next navigate down to the section "Events from Gmail":
Finally change the "Privacy of email events" from "Only Me" to "Private".
You'll still need to give individual people or specific Google accounts the proper permissions to view private events on your calendar.