From what I understand, this law does not normally apply to photo contests. But in this case, Asia Georgraphic is a magazine and it intends to publish the winning pixs, so they probably still need this.
Of course the law will not be so strict such that, eg, if you take a pix of 100 people, you need 100 model release signatures. But if you take one or a small group of people, you may be liable.
Also if it is back view, or from a distance such that the person cannot be easily recognised, again you won't need model release.
And I believe some other countries less strict. eg so long as photo does not portray the person in a bad / negative light it is ok.
But to be kiasu, best to submit only pictures of monkeys.
Anyway this is my understanding. Perhaps some lawyer can help to clarify further.