The article does NOT mention what armored personnel carrier was involved, thus the weapon could be a ,50 Caliber Machine Gun, a 14.5mm machine gun, a 23mm or 30 mm Cannon. All are design to DEFEND the Armor personal carrier from Air attack. These are NOT design to do an act of some sort of offensive nature to Aircraft.
Now, if an aircraft gets to close, all of these weapons can fire on and destroy attacking aircraft, but they can also be used to warn an aircraft it is to close. That the aircraft did not report any hits indicate to me, these were warning shoots, nothing more. The plane flow to close, so the Personal carrier fired a burst into the air at the plane telling it, if it came closer the Personal Carrier would defend itself.
The 30mm (30x165) has a range of 2700 meters in the AA mode, about 1 1/2 miles.
http://en.wikipedia.org/wiki/30_mm_automatic_cannon_2A42
the 23 mm (23x152B)gun, also has an 2500 m range in the AA mode
http://en.wikipedia.org/wiki/ZU-23-2
The 14.5 mm Machine gun (14.5x114) has a range of 2000 meter in the AA mode (3000 meters in the ground mode(, i.e. just over 1 mile.
http://en.wikipedia.org/wiki/KPV_heavy_machine_gun
The 12.7mm (50 caliber Russian, or 12.7x108 mm round) has a range of 2000 meters, but only about 1500 meter in the Anti-aircraft mode.
The Russian have used all four rounds since the 1960s. The 23mm is older then the 30mm, the 23mm dating back to WWII, the 30mm only to the 1970s. 30mm provides greater range and more powerful hit, but at the cost of the need to replace the barrel quicker.
The 14.5 mm is heaver and more powerful then the 12.7mm round (Both developed in the 1930s as Anti-tank rounds). The 12.7x108mm round, like the .50 caliber US round (in metric terms the US .50 caliber is referred to as 12.7x99mm round) was developed from late German WWI .50 AntiTank rounds. By the late 1930s the 12.7 was no longer considered powerful enough against tanks EXCEPT in a machine gun, the series of rounds hitting one point of armor would crack through armor that was able to take one 12,7mm round. In the US the US decided to stay with the .50 caliber machine gun as its primary anti-tank weapon, to be supplemented by 37mm cannons.
The Russians opt for a combination of 12.7mm machine guns and 14.5mm anti-tank rifles. In combat the 12.7mm machine gun was heavier then the 14.5mm anti-tank rifle, thus the choice came down to 20-30 rounds from the machine gun or 3 to 4 rounds from the Rifle. In 1941 both were found to be effective on German Tanks, but as Germany adopted larger tanks the Russian had be abandon both weapons as no longer effective against tanks.
On the other hand, the Russian found both rounds excellent against air craft and other vehicles and targets (The US also found this out, keeping the .50 caliber Machine Gun for the same roles). Thus starting in WWII produce machine guns in both calibers. The 14.5 Anti-tank rifle was shifted to other uses (mostly against other targets). Thus after WWII, along with the 23mm round, the 12.7x 108 and 14,5x114 mm rounds were used in aircraft and on vehicles for protection from air attack.
Please note, for weapons under 20mm it is illegal under international treaty to have explosive rounds. Thus the 12.7 and 14.5 rounds were always full metal jacket or Armor piecing rounds, with no explosive contents. The 23mm and 30mm rounds can have explosive loads and thus have explosive warheads.
I bring this up, for this still sounds more like someone flew to close and was fired upon to tell that pilot he was to close. I expect this was tracer ammunition, so the shooter can see where the rounds were going, and the pilot can see where the rounds were going. Thus I suspect this was 12.7x108 or 14.5x114 rounds (and maybe 7.62x54R Rounds from the anti infantry machines gun that are also on those vehicles).
I doubt it was 23mm or 30mm rounds, mostly do to those rounds being explosive and thus better kept back if the plane did decide to attack. Thus this was just a warning not anything more.
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