I'm not a military expert so i don't know what "peace configuration" means exactly in terms of organizational structures (BTGs vs brigades, and so on, i'm not into all these technical details), but what the article says about Russia entering with a very small force is true and has since been confirmed even by western sources.

As for whether or not the article is credible, that's up to you to decide but i'll just point out that all the article really does is cite Ukrainian sources. You are free to disagree with the analysis but the facts are what they are.