It’s not a conspiracy, it’s a pop culture reference. Very unlikely it’s unintentional, given that Thinking About Roman Empire was a fairly notable meme of ‘23/‘24 (https://knowyourmeme.com/memes/how-often-do-you-think-about-...).
Could be not a primary cause for the naming - only authors can tell - but I doubt they missed the reference entirely. It’s just way too obvious.
If you've learned even a little about the history of Rome then you'll quickly bump into SPQR, Mary Beard's recent popular, and very good book on the Romans it titled "SPQR", in the city of Rome you'll see SPQR used all over, in films when Romans are depicted, SPQR is always there. While not everyone will have a background where it's familiar, it's also not at all obscure. If you're not familiar with the Romans you won't know, but lots of people like to learn about the ancient past since it's really interesting to some types.
I dunno, SPQR is fairly obvious for anyone who covered Rome in elementary or middle school history.
Beyond that, if you’re from the part of the world where asterix comics were popular (mostly thr francosphere, but also europe more broadly), it really stands out.
That’s all to say nothing of people who’ve got formal higher education in history or even the classics.
I am struggling to believe that the Roman Empire reference for this acronym is "so obvious". I do know about the meme: in fact, what struck me so hard about this is how, for a protocol where you'd almost expect it to be hard for them to avoid the acronym "SPQR" (as, even if it were not Sparse, it is made by Signal; I could even see them having started with Signal and decided to remove their brand from the acronym), there are not one but two top-level posts on Hacker News where "speaker" seems to have wooshed over their head and somehow this extremely niche acronym from the Roman Empire is clearly the reason why this is called SPQR. Is the tech community on Hacker News really this stereotypical?