I would be unsurprised if it's true. The reality that DDG is going to have is that search is almost inherently personal, as an artifact of the imprecision of language and the lack of surrounding context. It applies to some searches more than others, but something like "what is vanilla?" Has a whole variety of answers. What is the substance vanilla? What is made out of vanilla? There's probably 80 different software frameworks that use vanilla in the name. Who knows how many companies have vanilla in their name. Oh, or it could be that you mistyped Manilla, which has its own set of results.
Personalization let's you cut down on that. Maybe this person searches for Python stuff a lot, so there's a good chance the frameworks are what they're looking for. Or, the inverse, this person looks up recipes all the time, they probably know what vanilla is so don't show a full page of "this is where vanilla comes from" results.
Lacking that context, they have to assume the same context for everyone, so either everybody gets a full page of web frameworks or everyone gets a full page of frameworks; DDG has no way to tell which you're probably more interested in.