I feel like Legosi wasn't JUST being a dumbass, but he was just handed the perfect foil for himself. Like, legosi isn't the brightest for one, but hes also naive. That fact about him had always been clear, especially in his duel with Riz where he tried to see where he was coming from despite their differences.
There was just too much for him to avoid in this case. Knowing that hes a hybrid and meeting one for the first time would be jarring in itself and make him feel kinship all on its own but this hybrid guy is already known to be a good manipulator so obv he would be pulled in easily with the allure (even if it seems like he was swayed too easily in my opinion... like bro where is your skepticism, that guy is a criminal ffs)
Anyway, I do think the reason why he was swayed over is obvious but I dont think the scene was executed that well given how it just makes Legosi look like a dumbass (which, to be fair, he is one) but like to an extreme. I think he shouldve shown a little more hesitance despite his willingness to listen to this hybrid criminal.