Yup what MC just said did not make sense, though someone being so blindsided by some random flattery is not completely unbelievable.
Basically that guy has to be real dumb for this to work but it could actually work if that was the case.
People are more likely to "let their guard down" when they think they have complete control, MC makes good use of that to magic up (he had to have applied it in full view while splitting the bread, without poisoning his own piece) some poisoned bread before idiot comes back to his senses.
And for once I don't think he spoke in a way that would have worked, but that might be because of how their words and honorifics work.
The main problem I have with this chapter is that MC just buried him in what looks like loose dirt, he does not seem to have flattened it or nothing AND ontop of that the guy is a martial artist, well trained as all hell, there's just no way MC can be sure that will hold him even for a few minutes, unless what, hes going to shank him if he tries to undig himself?