'cuz he saw sunbie being close to Ji Ho and he knows sunbie is using Ji Ho to get closer to Hyeon ui
When actualy…Ji Ho & Sunbie has a win win situation (Sunbie wants Hyeon ui, Ji Ho needs a home

)
So thats why Kang Dojin was unreasonable (he was too jealous to even think straight and lashed out just cuz they were close & wispering to each other, he shouldn't have done that ofcourse…not to mention he is also living in that exact house)
and then the mob came and enjoyed the drama
and Hyeon ui came to make the situation more complicated lol