The highlighted is obviously a lie though. Baldur's Gate 3 does not have a proper reaction system, and comments by Swen/Larian have heavily implied that they are still working on the reaction system to make it work better with 5e. But how can they simultaneously have had "ported [5e's reaction system] to the computer game" and yet, 1 year after EA release, 2-4 years past initial development, still have a reaction system with less functionality than tabletop that they're trying to make work more like 5e? Shouldn't they just able able to use that original build?
Not necessarily no. There is something called "prototyping" - trying things out in a quick, cheap and easy to impliment way to see what works and what doesn't. Of course, Larian didn't create fully produced, fully working faithful 5e translation which they then started to change - that would be a massive waste of resources. But it doesn't mean they didn't do some prototyping. Maybe in their own engine, maybe in one of the free, easy to mod ones (like Unity). It's possible they didn't implement everything into one build, but rather created different experiements when considering different mechanics.
