This is also why update signatures should be validated against a different server; it would require hackers to control bother servers to go undetected
No, it should be a hardcoded key held by the developer, preferably using a HSM, and maybe with some sort of notification capability in case the key was lost. Adding a second server adds marginal security. For instance if the developer's mail was hacked, an attacker would likely be able to reset passwords for both hosting providers.
notepad-plus-plus.org currently has an A record of 95.128.42.184, owned by "Aqua Ray SAS".
It switched up from 191.101.104.10 and 212.1.212.49 on 17/1, which is are Hostinger IP addresses.