Used once is referring to plastic bags used to hold groceries and then immediately thrown out. (Not used more than once: ie a garbage bag, pick up dog poop, etc)

So it is comparing 1 reusable bag used 131 times to 131 plastic bags.

Further in the article another study considers plastic bags used more than once, which are much better for the environment.

>I think the fundamental problem with plastic bags is that since they are 1 or 2 use, they are always going to be entering the environment at a rate faster than they degrade. So there is going to be an ever-increasing buildup of plastic bags in the environment for as long as they go on being used.

I think it is much more important to look at scientific studies than what a random person hypothesizes with no evidence to back it up.