This calendar may appear to be coming from Hebcal, but it's not hosted by hebcal.com
Likely the cause is that somebody downloaded a copy of the Hebcal calendar, added their own personal events to it, then accidentally shared it openly on Google Calendar.
To find out how to remove this from your Google calendar (and whom you should contact to let them know that they inadvertently may have published their personal calendar openly), try this:
Hope this helps!
Customer support service by UserEcho