Niara,

Blimey, you can certainly ignite a few candles just by looking at them. However... after re-reading that line several times, I got a suspicion of some sort, and I'd like to verify it. So, let's try to split that particular hair one more time, shall we? Original quote, courtesy of Composer / Ragnarok (I believe this is the one that everyone is talking about? Otherwise, all bets are off):
Originally Posted by Swen Vincke - Source from October 2020
BG3 is based on the fifth edition [of D&D]. We started by setting out the ruleset very meticulously, and then seeing what worked and what didn’t work – because it is a videogame, and D&D was made to play as a tabletop game. So for the things that didn’t work, we came up with solutions.
The first sentence seems pretty standard, and doesn't raise any alarms, per se. Pretty much every DnD CRPG is "based" on its corresponding ruleset - no one, in my memory, ever claimed that their game implements 100% RAW, however simple that edition might have been.

Going to the next one, and this is where things become hairy (pun intended):
Quote
We started by setting out the ruleset very meticulously, and then seeing what worked and what didn’t work – because it is a videogame, and D&D was made to play as a tabletop game.
"Setting out"... I always have had a great deal of trouble with this peculiar English thing, when a preposition completely alters the typical meaning of a preceding verb, because my native language doesn't have any of that tomfoolery. So I asked google what it means, exactly, and this is what I've got:
  • 1. begin a journey.
  • 2. arrange or display something in a particular order or position.


Clearly, it can't be #1, as 5e has existed long before Larian has put their greasy hands onto it. So... it leaves us with #2, innit? And that means, if I'm not mistaken, that your description
Originally Posted by Niara
of what actually occurred - which is that, at best, they read over the 5e manual and set it down on paper in a bullet point form as short hand, and then went to their game engine and started seeing what they could build into it from that list.
is not just exactly what they did (I don't think anyone still doubts that, not at this point), but also is exactly what they said.

However, the rest of that sentence is a pure misleading, and you nailed it perfectly. When they say "and then seeing what worked and what didn’t work – because it is a videogame", they couldn't have meant the entire videogame genre in general, they meant D:OS2 engine. Because if it was about a genre, then Solasta proves them wrong on all accounts. As such, your statement:
Originally Posted by Niara
It did not, at any point where game implementation is concerned, ever start out as a meticulous setting out of 5e, was not, ever, tested as such to determine what did and did not work in a video game format - and to claim otherwise, or to word your language in a way that insinuates otherwise deliberately, as they did, is misleading and dishonest.
still stands, I think.

The last sentence is, again, a banality. Everyone did it before them, there's nothing new here.

TL;DR: So, basically, it all boils down to a single word - "videogame". Swen used a generic term, while having a very specific one in mind.