"Charter of negative liberties" is a good phrase for this discussion. There are certain things the government cannot do to you. The police are government actors. Here, they possibly did one of the things that the constitution proscribes, per the relevant case law defining the reasonableness of searches and seizures. "Cuffing" (here, arresting) a suspect is a seizure. Of note, "cuffing someone" is not the issue. Making a public spectacle of the arrest is the issue. While this "perp walk" thing is arguably a low priority constitutional violation, it might give us a sense of the esteem in which the local PD holds the constitution as a guide for their routine searches and seizures (and, currently, there is an issue regarding their use of checkstops in minority neighborhoods). That's kind of a big deal and, beyond just Evander, it impacts citizens of Erie County who *don't* have similar wealth and status.
Raising that issue is not problematic or "interesting" (in the pejorative sense, as you've used it here) - rather, it's good citizenship.
Most importantly, none of the above has anything to do with "Evander Kane" as a person or a hockey player. Your opinion about the man is yours - but it's irrelevant to this question.