The escorting aircraft would not need to fly side by side with the passenger aircraft. They could just fly behind, above or bellow the aircraft quite easily and not be seen by anyone on the aircraft.

Not to mention that Air to Air missiles have a range in the tens of kilometers and the MIG-29 has sensors to observe the aircraft up to 100 km away.

I don't think any of the passengers would have been aware in the slightest if the MIGs where flying 5 km behind the passenger aircraft.