Can some supportive words in psychotherapy reinforce one's psychopathology?

It can, but depends. Therapists should rarely, if ever, purposefully use 'punishment.' they also cultivate supportive acceptance of clients. Sometimes that even includes very unusual topics. However, acceptance is not 'encouragement.' when pathological behavior presents itself, the therapist should accept it but avoid rewarding or punishing. If the client can take it, the therapist also points out the behavior.
Misperceiving or . Misinterpreting someone's comment is common in human interaction and is a core part of some psychopathology. A good therapist will easily work with unintended consequences of a remark. However, if a therapist is consistently making your problem worse and you've told that to the therapist, find another therapist. You need to find the right style of therapy for you and be willing to change.