It may have frozen, but I doubt that it's ruined.
Can you thaw it with a hair dryer?
Today for the first time my stock hydrant ( type with 1 inch pipe appx 4 foot out of ground with pull up handle) would not open. We've had colder nights down into the teens without problems.
Does this mean this hydrant has frozen and needs to be replaced? This one has been in-service for 4 years.