You are absolutely correct. William Sandy, married to Catherine Beck, never resided in Virginia, and was the son of a Jared (or Gerard, etc.) Sandy. William is mentioned in Jared's 1794 will. It appears to be likely that Jared Sandy was born in Virginia, and was probably a brother to William Sandy, husband of Dinah Wood.
These different William Sandys are frequently conflated, but were very clearly several different people.