I agree is it logical for Paul to make those judgements and say those words, but Rudy still had no idea the teleport spread that far. They were at the very center. So what else was he going to do?
Paul's messages were everywhere? Bullshit. Paul says they were posted at Wind Port (the demon continent's only port), but Rudy's limited knowledge was that they were the only ones sent away. Dead End arrived to depart the same day that Roxy's party with Paul's former members arrived. My bet is that the dwarf reposted the message there.
Paul just jumps to conclusions like he always does.
Rudy is hurt even more by this because Paul is essentially betraying him. In his past life, all his family ever did was criticize him. Justifiably...maybe. But the trust Paul had in his son, enough to send him away on his very first job at a young age is just ripped away from Rudy and suddenly nothing Rudy has accomplished the entire year and half means anything because Rudy didn't do what he should have, even though he wouldn't ever have known. So Rudy is taking the blame for something he absolutely shouldn't. Rudy's past life patterns return in force, throwing up out the window even thinking about talking to Paul about it to calm him down.
This is why Eris' rage upon seeing him down in the dumps is so moving. She sees his wounds but more importantly, the beaten way he's acting and immediately flies into vengeance mode.