It's a more specific offence, but it acknowledges the fact—and it is a fact—that torture takes place. It's relatively rare, thankfully.
Let's think of the standard understanding of torture. It's the imposition of severe physical or mental pain onto another human being. When that has happened, then it needs to be acknowledged. Also, if it has happened, then it's up to the crown to gather the evidence that would allow for the offence to be prosecuted.
In terms of burden of proof, you pointed to a potential problem with how the bill was originally written. I've made a revision. If you compare page 1 with page 2, I've dropped the word “official”, basically, so that we're dealing with a generalized torture offence that applies to every person.