It makes perfect sense. Because the Iran deal, at least according to Trump's read, states that Iran's nuke facilities must be protected from attacks. This apparently INCLUDES US protection! Russia has recently installed anti-aircraft systems in Syria, yet neither ISIS nor any of the rebel groups apparently have aircraft! So, obviously, the anti-aircraft weaponry will be used for 'other' purposes, such as, perhaps, helping prevent an Israeli air attack on Iran nuke facilities, or at some point, helping protect them or their interests there (the Russians' and/or their Syrian allies) from NATO air attacks.
Not right—If Israel attacks Iran, they will send their airfleet south over Saudi Arabia and attack by flying over the ocean. Maybe refuel in Arabia? As Subs launch Missles to aid in the attack. No need to fly over Syria.