As someone who knows nothing about this, I would have expected some sort of maneuver from the targeted aircraft. Wouldn't a modern aircraft have some sort of threat detection that would alert the pilot to take immediate evasive action?
Unless its some missile active radar, or semi active radar. This missile was likely a fim-92 or sa-18, meaning it tracks heat emissions and doesn't emit any signal, so there is almost no way to detect it. There probably are systems to detect a missile launch of this kind, but those systems are probably classified and I don't expect the russians to have it.
There probably are systems to detect a missile launch of this kind
Some aircraft have missile launch detectors that are based on detecting sudden IR blooms in their vicinity. I don't think many aircraft have them though.
The Su-25, the aircraft in the video, does have a rear-facing IR dazzler. It basically shines an IR flashlight into the 'eye' of any missile following the aircraft. This IR missile, however, hit it from the front/left and not the rear, so that dazzler had no opportunity to attempt to confuse the missile.