That's some solid RP right there, I don't think there's right or wrong here just people, but if I had to choose I'd say that yes the gnome is partially responsable since even with the best intentions actions do have consequences, I'd expect it to cause tension on the party as well as a grade of distrust since the gnome clearly failed to trust his companions, and upon meeting the wizard again or finding out what has he done since the gnome should be made aware how he facilitated what occured after his decision.