This is what we at XenFans used to debug a custom resource that someone has installed, but we don't know where it came from or what plugin it might be, or which templates we're looking for.
I would temporary add debug mode true to the config.php file of XenForo, then add the custom url with ?_debug=1 at the end.
I'd scroll down to the bottom where it has a list of internal_data/templates/S.8,L.1,SOMETHING.php, and looking at the custom url, if it would be 'banana', to look for the SOMETHING to match banana (as it usually does). Then I'd turn off debug mode, go into the admincp, and to templates, and enter the found template in the search field there and open it. Hopefully finding what I was looking for.
The reason I offer this as a possible solution to figure out where is what for this custom page, is that I suspect the word 'page' here is what gets confusing. Your site has /pages/ and this particular 'page' on your site does not have the prefix. Implying it's not a node, and that's why it returns with NULL. XenForo has four types of nodes, for links, category, forum, and page. They have their own prefix, unless a route prefix is rewritten or whatever. Your site reflects this, but not this custom 'page'. Which is just a normal website page, it doesn't mean it's a node with type 'page'. They just coincidentally (i suspect) have the same name. I suspect that this is a custom plugin with a template with a callback to some php that reads in the reviews etc.
Maybe the debug trick will help you find the templates, and when you edit the template it should disclose which plugin is using that template (the debug page can also disclose this btw)
I read through the thread here, but am a bit confused as to what you're trying to actually do on the page. Rephrase a word? Add new html to it? Anyway, based on what you want, and knowing which plugin is making this custom website-page for you, might help you figure out where to either customize the phrases, the templates, or how to manage it's content that it seems to dynamically generate.