Native speaker here - it wouldn't really cause me much pause to read that. I would assume the author is exhibiting some style.
While you're correct in your assessment that the structure is grammatically incorrect, you might be focussed too hard on the ideal of grammar rather than realising that grammar describes the language, it doesn't prescribe it. If a native says it, and intended to say it, it's native speech.
As an example, I personally enjoy using "for sure" as an intensifier, but injecting it into an off-beat part of the sentence. "That's the right attitude for sure" has become "that's for sure the right attitude".
Were I particularly interested, I'd read the authors other works to get an idea of their writing style and see if they experiment a little elsewhere too. If they do, I might find some experimental techniques I'd like to use myself sometime. If they don't, I spent my spare time reading in search of knowledge.
Your English skills, judging by your post, are rather strong, so it's not going to be detrimental to your learning journey to encounter experimental playfulness done by native speakers. Doubly so because the colouring outside the lines catches your eye and spurs you to ask questions like this. Even if you happen to accidentally acquire something that's not technically correct:
- it's easy enough to unlearn lingual habits mistakenly picked up; and
- a native said it so it is correct.