VoIP fraud is very sophisticated and it's not just about toll fraud. The author uses a small snapshot and tries to suggest scenarios. However, that's like the one-shot case study that shows all clover have 4 leaves and are sometimes green. You need much more data (and investigation) to make any proper conclusions.
Often the multiple calls a denial of service - frequent numbers are often large companies being subject to a denial of service (the US embassy is a popular target) or they are test calls to verify a server works (i.e. call their own number and listen for audio) before pimping it out for toll fraud.
The PA ones could be a mix of that plus the more sinister DoS block on targets about to be attacked to prevent them calling for help.
There's a list of hack attempts over a much longer period available at https://network-systems-solutions.ca/voipblocklist.php That gives a bit more meat for anyone interested in looking for patterns (or protecting their server I suppose)