SS7 I am sure is hack-able, but its a point to point link between 40 year old telecom switches. Its not easy to find or access, and you would need a bunch of other equipment to actually do anything useful - like send a call through where one could intercept it. These testers had such access and equipment, and I am sure the govt does to. The average hacker? No in your life. Most would never have heard of SS7, since the protocol and network are 100% divorced form the internet. The Mobile network uses SS7 eventually, but then its the same deal. Getting access would be a pain. Using that access to do anything would be even harder.
And They hacked a phone, and all they had to do was get someone to download and open a text from someone they didn't know on a phone they prepared for the purpose? OoooH. Scary.
Looks like someone was trying to justify their funding.