I agree, this sounds like sour grapes from HPE as they wanted these witnesses to testify.
In civil cases, to prevent the trial going on and on forever, often a judge will limit the number of witnesses both the plaintiffs and defendants can call. For example, the judge may say that each side is allowed to call 10 witnesses (usually excluding the defendants themselves from the number of allowed witnesses if they choose to testify).
So, it sounds like HPE decided to not call these witnesses and used their allotment to call other witnesses instead, because they could question these ones under cross-examination as the opposing sides witnesses, thus not using up their witness allotment on them but still being able to use them, having their cake and eating it.
But now, the defence has decided to not call them, thus potentially harming the prosecutions case. Very nice tactics from the defence if that is indeed the case, and a total balls-up, a miscalculation, from the plaintiffs. HPE lawyers have no-one but themselves to blame. They took a gamble to be able to, effectively, have more than their allotment of witnesses, and they failed.