Fujitsu may not be liable merely for there being faults in their software, but they should definitely be liable for participating in the lying and cover up of those faults, denying that their engineers were able to access subpostmasters systems remotely etc.
As the Computer Weekly article below points out:
Fujitsu to finally face blame for its part in Post Office Horizon scandal
So basically, what the judge was saying was that Fujitsu representatives lied in court. And for that, they should be held accountable.