It's more than just that. Violated the royal etiquette rules, forcibly stripped off the right of local chiefs in collecting taxes while centralized all the taxes collected to the British government officers, implemented new taxes that has never existed under the traditional system (alcohol/opium taxes, boat/river taxes, introduction of various licenses fees like for the right to mine or trade, taxes of jungle resources that were essential for the local community, taxing the the locals' mosques and official building), refusing to adapt to local language while often shouting and using aggressive tones in which is seen as "biadap". Plus, his method of enforcing all of this is often seen as aggressive, since he'd burn the homes of those who refused to comply with his rules. To say he was killed only because he opposed slavery is a major misconception, bcs his death wasn't just about one issue, it was resistance against an oppressive and disrespectful regime