Come on ...
1) There is no evidence that those travelling on lost/stolen passports were using the 72 hour visa-free policy. Both could have simply been international transfers, intending to remain in the secure area of Beijing airport.
2) There is no evidence that China visa screening includes an Interpol check for lost/stolen passports.
3) As of now, there is no evidence that this was an act of terrorism. Illegal passports are used for many reasons.
Raising the 72-hour visa-free policy as an implication of an "open-door" policy is misguided hyperbole. It seems if there is a need to assign blame, it should be levied at the embarkation point (i.e., Kuala Lumpur) for permitting these passengers on the plane in the first place.