>Isn't this essentially the Trolly problem, If a trolly was going to kill a thousand people then Geralt wouldn't pull the switch to kill one person instead.

No. That is being forced to choose between bad outcomes, not two moral evils. Choosing between two evils would be, say, choosing between supporting a trolley conductor who wanted to run over one specific person he hated and one that wanted to run through a crowd to rack up a high kill count. The correct choice would be to support neither, since both are evil people.