As the article points out, peering rarely involves money (and shouldn't ever; as the word peer implies, its a largely symmetric relationship).
The ISPs' customers are paying the ISPs for bandwidth and then requesting traffic. Level3 is providing said traffic and then the ISP drops it because they don't have enough bandwidth. How can a reasonable person possibly interpret this as being Level3's fault?
If an ISP isn't willing to supply its customers with the bandwidth that is being paid for, they need to either fix that or stop promising things they aren't willing to deliver on.