Both sides in the conflict spread disinformation. DDG desides to downrank only results related to disinformation from one side. This makes it a decision based on a political bias and not search quality bias (which would cause all disinformation to be downranked - which is OK and actually a desireable thing in a search engine). By not downranking disinformation from the other side, which is equally bad content, this steps out of the scope of what a search engine should be interested in doing.

Secondly, how in the world would DDG have the resources or capabilities to determine what is disinformation in the first place? Much larger companies like Facebook failed at this. It is generally considered that the 'fog of war' is a real thing and there is no single source of news on this planet that did not spread some disinformation at some point. DDG would probably have to downrank half of the sites in its results, and probably every site that ever published any information about this conflict, if they were to be consistent. Something like this is basically unenforcable from an engineering/algorithmic standpoint.

So basically from a business perspective, this has to be a bet that the publicity from this act would net them more users than they started with in the markets they care about.