Part of the reason this is so bizarre is during the Cold War, the F-14 was specifically built to intercept and destroy Russian bombers seeking out the aircraft carriers in the North Atlantic. The US retired its F-14s about ten years ago. However, the Iranians were the sole export customer under the Shah. When the revolution came, the Iranians did a surprisingly good job of developing replacement parts since we were unwilling to export anything of the sort to an enemy.
Now the Iranians are allied to the Russians, at least as far as Syria is concerned and the Russian bombers need to cross Iranian airspace. So, they get an escort. This time it was an oddball situation with the plane meant to kill the others escorting them.