Acceptable in moderation
If the question is specific and answerable (i.e. passes the 'not a real question' test) and is on-topic per the FAQ then it would be on topic. One could probably envisage questions within these criteria that could be viewed as trivia in a subjective judgement.
However, the FAQ does not explicitly include 'database trivia' as being in scope, and the only redeeming feature of a trivia question has is that it's answerable. The PostgreSQL turtle question is certainly not within the definition of any of the major categories within the FAQ, as it is sociological in nature and discusses a cultural issue in Japan.
The important point is the cultural significance of the elephant motif, not the fact that the PostgreSQL team chose to re-brand the system in Japan with a turtle. It is almost completely immaterial to any technical database design, development or admininistrative concern.
The odd 'interesting' question is not going to hurt dba.se, although polls, code golf and various other types of populist questions are discouraged as they dilute the value of the site and provide opportunities for gaming rep.
I would consider occasional 'interesting' postings acceptable by the grace of the user base, but spamming populist questions should be considered disruptive behaviour at best, and rep gaming at worst. Spamming large numbers of poor quality or off-topic posts is widely considered to be unacceptable behaviour on the SE network (with good reason), and there is no reason for dba.se to be any more tolerant of that.
While interesting, trivia questions are not explicitly on-topic on the dba.se site, and sit in a subjective area where the discretion of the moderator community has some leeway to make a judgment call based on other qualities of the question.