Photos - "You have a new memory"
Hum...
Even though I think your question is actually not a real one - you seems to know that Apple tried to implement a Facebook-like feature and made it impossible (or really hard) to disable, a piece of answer is that Photos is not designed (in my opinion) for a professional use.

Photos is intended to store photos of your family, your friends, your trips and holidays or other annoying every day's stuff like that. Every feature is design in this purpose: moments, collections, faces, locations as well as shared albums and ... memories!

I'm afraid you only have few solutions available including turning of memories notifications you mentioned (and never tap the memories album again). If you don't want [your] professional environment besmirched by 'social media'-type actions you may have to choose a different photo app to separated your professional and private life.

Concerning the algorithms behind memories, it is obviously based on similarly between groups of photos (location, date, people...). From my personal experience 2 différents types of memories are highlighted by the App: 


Regular memories that gather photos from a recent event (a trip, a week-end, a party). They are usually pushed froward few weeks after the event ends.
Special memories that are usually highlighted many month (sometimes years) after the event ends. Such memories could contain only photos of a specific person (the memory titles "[Person X] over the years", "[Person X] birthday", [Person X]'s Home) or photos taken a specific amount of time ago (a have a "5 years ago" one, here are some other examples: "last Winter", "On this Day", "Chrismas day", "Halloween" and even "Best of Last Week/Mounth/Year").


I guess that you dislike this second category. This is quite intrusive I reckon but Photos App IS a social App since Apple designed to encourage photo sharing and viewing between family and friends rather than for professional use.