Not true, Amraann, though MacDonald's supporters have repeated that claim so often, it's no wonder most of us can chant it by heart.
The publisher's insurance company forced a settlement in the middle of the trial before the case went to the jury. This is pretty common and I have personally worked on cases where a resolution was imposed in that fashion.
Basically, all big companies carry litigation insurance and the insurance company has to pay the cost of trial and any judgments. All policies for litigation insurance include a provision that the insurer can force a settlement if the offer is lower than the costs of continuing. So if finished the trial will cost $1 million, say, but the plaintiff is willing to settle for half of that, the insurer can demand that the settlement be accepted. (If the insured refuses, the insurer is off the hook for any additional costs.)
This is what happened in MacDonald v. McGuinness, and the writer still believes the eventual verdict would have been in his favor. But the doctor's supports like to claim it as a victory.
But the issue in that trial wasn't actually the truth of the book. It was a suit for breach of contract. The doctor claimed that the writer misled him by claiming he believed in the doctor's innocence. The writer responded that he started out believing MacDonald was innocent, but changed his mind after he was given access to all the evidence. MacDonald claimed that the writer should have announced it as soon as he changed his mind and that failure to do so was fraud. That was the issue before the jury when the settlement was reached.
MacDonald's supporters also like to claim that the writer "was forced to admit" under oath that some things (including the possibility of amphetamine addiction and rage) were speculation. But the matters they cite for this purpose were clearly described as speculation in the book itself; or at least it was always clear to me.