It's not uncommon for Owners to be pissed off by their own cheaper-now decisions. The Owner and the Contractor spend all day on site talking about how stupid the Designers were...which is easy because all their mistakes are right there on paper.

Anyway, the Owner's underlings are the Owner if they have the authority to approve changes.

And if you saw the Owner pissed off, then it is not unlikely that they are the sort of person who blames others for their errors.

As for the distribution of the money, everyone probably got some except the Design team...it's the sort of change that the Owner and Contractor collaborate on despite the professional opinions of the Design team. And so the Design team can wash its hands of responsibility since they did not get paid for the extra work of changing the design (which is why the design documents differ from the asbuilts).

Or to put it another way, with any substantial size building everyone was sitting around the table when the option was discussed and the Design team walked the site prior to approving the Contractor's pay requests for plumbing labor and materials.

There are lots and lots of checks and balances in even below average construction projects. Swapping PVC for copper throughout is not the sort of thing that goes under the radar.