I would definitely call it misrepresentation - which is a failing on behalf of the company - and not misinterpretation, which would be a failing on behalf of consumers.
When taking individual quotes out of the context then perhaps - it is of course difficult for me to get into the shoes of other people, and how much exposure to the title they had before they bought it. That said considering that the game's prerelease marketing came packaged with multiple lengthy gameplay presentations showing precisely what kind of a game BG3 is aiming to be, I find it difficult to blame Larian for the misrepresentation of their game.
This interview already discussed significant changes, like reactions, that sparked flames of discontent on these very forums months before EA's release.
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. The initial days of the game made it clear that the engine was almost entirely lifted one to one from D:OS2, and then modified From There to have more 5e bits and pieces, and that process is still on-going.
I don't think we will ever know how early in the development Larian decided to deviate from written rules - but I am willing to agree with you here. I do think it's likely that Larian planned to make some sweeping changes from the get go, and keep some signiture mechanics from D:OS2. As to the engine - it IS significantly different then D:OS2. Sure there are similarities, but ruleset wise it is a different game from D:OS2 and could be even more different if Larian wished for it to be so. Games don't need to switch engines to be different. And again: same interview I mentioned before openly discussed Larian's philosophy on adapting 5e:
They (reaction) are a topic that illustrates very well that sometimes you have to target the feelings that the rules are trying to induce in the player, instead of trying to follow the rules letter by letter.
Then he goes on to explain the reasoning behind the change. I think we both agree that this change (and some others) aren't for the better and don't properly substitute tabletop ruleset. But misrepresentation? Nah.
