It's impossible to tell if someone is genuinely making mistakes or simulating them, but just from a surface analysis: I don't think a native speaker would ever

It's impossible to tell if someone is genuinely making mistakes or simulating them, but just from a surface analysis: 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.