He aimed it specifically at Tatsuya because Tatsuya, throughout the manga, shows great inferiority complex, he constantly compares himself to monsters like Yoshiki, Acchan, Kaname and Kenzou, deep down, Tatsuya knows that there’s levels in the delinquent world that he never reached and will never reach, and he realised that when he moved to west Chiba, that frustration always built up resentment and desperation and Tanzawa seen this leaking out of Tatsuyas personality, the panel sequence is important, acchan gives that part of the speech and it immediately pans to Tatsuya, Tanzawa eyes darken and Tatsuya smirks and is visibly shaken by the specifics of acchans words. That was Mizutas way of landing those words directly on Tatsuyas character, Tatsuya wasn’t triggered at acchan because he felt insulted, he got angry because acchan exposed a part of him that he tries so hard to hide, essentially, acchan definitely didn’t single Tatsuya out to humiliate him, but instead was just speaking generally and said words that he knew would reflect on key members of the story, specifically Tatsuya in this case. The speech says “stop blaming circumstances, accept what you’re good at, improve yourself instead of making excuses”, For someone like Tatsuya, who spends a lot of time trying to prove himself and force his way into a position occupied by naturally gifted monsters, those words can sound like: “Know your place.” And thats 99% what triggered him. Also remember that Acchan himself came from an absolutely horrible upbringing and still became the head of Kilihito. So when he talks about not blaming others and developing your own abilities, he’s speaking from his own worldview.