Hello there,
Technically, it is possible to improve rankings working on other site. Thar could be only and only because of links pointing from the site being worked to the site to be improved. This is not mathematics, it could work, but there's no garantee.
Im sensing that you're not fully aware of the reasons that would rank a page and even more, that you've skipped reading some resources like:
Begginers guide to SEO - Moz Google’s 200 Ranking Factors: The Complete List - Backlinko.com Search Engine Ranking Factors 2015 - Moz.com How do I build the perfectly optimized page? - Moz blog On-Page SEO: Anatomy of a Perfectly Optimized Page (2016 Update) - Backlinko.com How to Build Backlinks in 2016 (NEW Guide) - GotchSEOc.com
On one hand the fact that adventurerooms get better results is, as you've said, that you've been working on it and there might be more links or a slightly better optimization.
On the other hand, when you say one is better than other in SERPS, is it for the same keywords? if it is for different kws, are they similar? What about the difficulty for those?
And you also should know that the moz's metrics doesnt strictly indicates that a site is better than other just for a few points in the PA or DA. That metrics, weights and correlates the link profile and some magic behind the courtings.
Hope i've helped.
GR.