His writing lacks the typical mistakes Eastern Europeans often make when writing English prose, namely omitting the indefinite article. If you look closely he might be overcompensating, for example:
I’ve already said about the software vulnerabilities
But I made some conclusions from the Marcel’s storyThe second example is, as you say, an obvious mistake.
I don't think a native speaker would ever say "I've already said about..." - you would say "I've already mentioned/written about/discussed". "Said about" is glaringly, obviously wrong.
In the second thing you cited, I could see that being a typo / editing mistake - could have meant to say "from the Marcel story" or "from Marcel's story" and it got mixed up in editing (e.g sometimes you write a sentence one way and then paste something in and don't re-read what you wrote). But if it was intentional then yes, it's definitely wrong.
I find it irritating when I read writing that includes those kinds of basic mistakes.
Of course, you even see those kinds of basic mistakes on the TV, especially the news tickers. I see about one per week, and I'm not even consciously looking for them.
I think it's people who have never read a lot, so they just write whatever sounds similar. Just seems lazy to me to not check, and after reading these comments from non-natives who can get it right, I now think it's super-lazy.