be won from a bonus roll, in addition to the standard bonus roll reward.
This is the typical confusing wording I've come to expect from programmers and engineers... but as I read it, you click your little icon, it rolls a bonus roll. Then in addition to that bonus roll it rolls another bonus roll only to check for pet. The changes being you can get it from the main bonus roll that usually rolls for your loot, as well as your roll for 'hey do I get a pet?'. That's the only interpretation of this very clumsy wording I can see that would change how it works now.
Because as Quintessence said, we have reports from people getting this from bonus rolls. As in, they got either gold + pet, or item + pet. That's how I understand the change, now you could get gold/item/pet + pet in the bonus roll, while before the roll was only gold/item + pet.
The other way it could possibly be would be if that what they call 'standard bonus roll reward' is the roll they do the once a week, if that's the 'roll for pet' they do on your first kill of the boss regardless of coin spending when you kill the boss. If that's what they mean then yeah, in that case we will have been wasting our coins... which doesn't explain how people have (according to them) gotten the pet from their bonus roll.