While they may not be able to lock onto a NATO plane, a civilian 747 might be another story.
There is something bogus about this story, of course I lack the inside knowledge to say exactly what. If there were 20K of these bastards in one place it would have been a priority strike target for the air interdiction to hit. Without going into boring detail about target prioritization, the FIRST thing you do is take out anything that can interfere with your air dominance BEFORE blowing up random tanks and bunkers.
The high-bypass engines on a transport are cool emitters compared to military strike aircraft, of course military strike planes are capable of high-G evasive action to try to break a missile lock, and also carry a good number of decoy flares to pop like Roman candles at the same time they're turning to shake a heat seeker. But with 20K of the mofos, you could set up a strike alley and serially fire 20 of them at a plane and sooner or later you'd hit a damn' plane.
I am not buying the basic story. There may be some missiles, but I have no trust in ABC's fact-checking as to the 20K, and if they are Viet Nam-era
Strelas you would have to put them through a depot rebuild to get even half of them to fire at all, let alone actually track anything.