This is more like my own headcanon, but the reason I think Yuzan is so unbelievably pissed off more than usual is that the fluke infection victim referred to here is
Rosanjin, the one who taught Toyama-sensei (his own teacher and the only person he respects), and as stated in so many chapters ago, a real-life artist and gourmet (who actually inspired Yuzan's character) that Yuzan always wanted to surpass in everything.
While I'm not sure whether Rosanjin also taught Yuzan, I believe that, despite his desire to surpass Rosanjin, Yuzan very much respects Rosanjin as a professional and as an inspiration, and is personally horrified by the infection that killed him.
Although I think Yuzan would've been just as pissed if it were someone else who died and not Rosanjin, Rosanjin's death from liver fluke, I think, adds to those personal reasons for Yuzan to be so angry because he doesn't want to suffer the same fate as Rosanjin.
Yamaoka…I appreciate that your own feelings are confusing for you, but you DO let her cuddle up to you on plane flights for 8 hours. you should probably stop doing that if you don’t want people to get the “wrong idea”
I think this is because the author just characterized Yamaoka (when it comes to love) like your average shonen manga MCs, who are so unbelievably dense in romantic affairs, even when women literally started throwing themselves at him.
At least there's a bit of an excuse for Yamaoka (since he never wants to get married because of his shitty childhood due to Yuzan's abusive treatment of him and Yamaoka's mom — resulting in him being so unbelievably oblivious to certain social cues).
But I won't lie that sometimes I too want to blast Yamaoka in the face to tell him not to be so oblivious about love, so people won't get the "wrong idea" (even though said people have become very much insufferable, like Kinue and Noriko).