Yes, it was a spur of the moment impulse decision by someone who was known to react that way. Most people who knew Ruby said that they were not surprised that Jack reacted the way he did.
I think of the flight of three people, from Dallas, on November 23; two of whom only returned after Oswald had been shot.
John Liggett suddenly left the Oak Cliff graveside funeral of a family member when word of the assassination was related to him there. He had been gone for 24 hours when he came back to scoop-up his family, without explanation, and headed south. His state of high anxiety and chain smoking was immediately alleviated after having watched the murder of LHO from a hotel room. He then told his family that it was safe to go home, and they did so.
Igor Vaganov, also from Oak Cliff, was checked-out by police hours after the assassination. He then hopped in a car and headed to Philadelphia, not returning until Oswald was dead.
Larry Crafard, employee of Jack Ruby, who lived in the Carousel Lounge, woke-up Saturday morning, after spending the wee hours of the 23rd driving around Dallas with Ruby and George Senator, while Ruby did strange things, and fled Dallas by foot and thumb with $7 in his pocket. He was located weeks later hiding-out with an aunt in an isolated farm house in Michigan.
Why?