Well, they're an Arch Linux user which is a special case. On Arch and derivatives it's the user's responsibility to manage the system so this doesn't happen, configure cleanup daemons, flush package managers, etc., alternatively it could also be a misbehaving application which would have to be reported. Arch is for hobbyists who likes to do this.
On other Linux distributions, Windows or macOS if this happens it's usually an application not properly managing its cache.