“Blue Certified” means nothing other than a limited warranty; most dealers just pencil whip the inspection and put it on the lot. Even if they are aware of a potential issue they may let it go so that the Ford warranty has to pay to fix it later instead of it coming out if their used car budget.
There was zero reason to replace the oil pump; all they needed to do was test it with a manual gauge and they would have seen it was within spec.
If they’ve went through all the circuitry and connectors, I’m with
@Old-Raptor-guy that it’s likely a repeat faulty sensor. You may want to also verify that they replaced the oil pressure sensor and not the oil pump control solenoid, that would be the extremely stupid but you never know.