While I absolutely support @AnotherElk’s hesitation* (I’m not sure how “unique” those buttons are, see the FP4 silhouette), this would turn the FP4 → FP5 upgrade from incremental (what it seemed like so far based on just the pictures) to quite a big step in my eyes: USA – a *tad* bit bigger than Taiwan.
I have now added the actual introductory line from Murena’s post in my reply above because I think it’s also some sort of mini-hint that I based my speculation on. After all, “the most sustainable phone” … admittedly, I’m not exactly observing the smartphone market as a whole very closely, but I think Fairphone has a good case to claim that title for them (apart from the “Theoneyoualreadyown” brand, of course 
).
* Let’s not argue too heatedly … all three of us are on the same team 
P.S.: Fairphones CFO has retweeted the Murena tweet. Probability seems to increase significantly. I’m mainly unsure just about the number behind “Fairphone” now.