This sort of thing sounds weird to nonlawyers, but it's completely normal. The key is that the jury found all of the relevant facts; the judge isn't finding any new facts. The judge just decides whether the facts that the jury found fit the terrorism sentencing enhancement box.
You can vehemently disagree with Palestine Action activists goals, whilst simultaneously be horrified a judge can decide AFTER a conviction if it was terrorism related amd double a sentence.
Being able to class an offense as terrorism AFTER conviction without charging them with terrorism should bother everyone.
Any protest action that is now determined as trying to "change government policy" can have this applied.
So today it's Palestine Action, but next it'll be immigration protests, farmers protests, NHS, tax etc etc.