It's a question of stats, really - in any population with a constant probability of some event (i.e. a technical failure report), you won't see all of them having 2.5 failures. One (in theory) will have none, most will have a few, one will be a total dog. (this is what stats folk call the Bell Curve, nowt to do with Bell helicopters) G-MONX is obviously the one at the !!!!ty end of the graph; either because of chance or because the Airbus lineworkers had a bad day. The former is much more likely! All praise to Monarch for being honest, after all a fault's only a problem if no-one fixes it. (but the spurious GPWS must have set the pax crazy...)
(edited to correct factual inaccuracy)