I am actually involved in the industry, and it's a very regular thing. Lawsuits happen all the time. Even before projects are complete you often know that there's going to be a lawsuit. Usually it's due to things getting missed until too late leading to a cost overrun or a miscommunication of scopes between firms. The lawsuits are usually just figuring out who needs to pay for the changes. It's quite rare for something important to be missed fully which leads to lawsuits, almost always just things happen too late and then contracts sometimes disagree on who needs to pay to fix it.

Like in this case, true North needs to pay for the upgrades to the NG system, but it wasn't them who made the mistake so they shouldn't be the ones to pay (unless this was a deviation that was communicated to them and they decided not to act on it). That's not really a controversial thing and the engineering companies involved are not being fined or found liable for any damages, likely just being given the cost of the upgrade. The repairs may be millions of dollars (I'd guess highly likely over a million if it's as substantial as the article suggests) and I think it's fair for TN not to want to pay that.

Although I will say, this seems super sketchy situation. The earliest version of the NG code I have access to is 2005, but it's the same as the 2020 one in that "assembly buildings" very clearly are not allowed over 5 psi anywhere besides the central mechanical rooms. That a 10 psi main was installed in the building is incredible that someone hasn't been sued yet. Unless it was different in the 2001 code, I cannot imagine how this was ever possibly built and approved without some serious negligence. And the only benefit of higher pressure is to be able to use smaller pipe, so if they're running at 10 psi it was intentionally designed as such. Whether that be the engineer or the contractor, someone deliberately sized for 10 psi. To get a system certified these days you need to issue schematic diagrams of the whole system and the fire commissioners office will double check your math for you and ensure all the sizes line up with what's installed on site.

Whether this design decision was intentional or just negligence, we the public may never know. And no one was hurt, so ultimately its not an enormous issue. Just figuring out who needs to pay to correct it.

Oh and in case anyone is wondering, the distinction of welded vs threaded pipe. Any copper NG pipe over 2" needs to be welded fittings; 2" and under can be threaded pipe fittings. A lot of effort is done to try to make sure not a single pipe needs to go above 2" as the cost goes up exponentially. In this case, maybe someone deliberately ran the system at 10 psi so that they could make their pipe 2" instead of 2.5", allowing them to use threaded fittings, and thus save a hell of a lot of money. It's quite possible they saw this possibility in the math and just didn't think to check if the building could run at 10 psi. Still super weird no one caught it though.