Changing the default password for the local administrator account on a VPN appliance is a basic security measure that would have most likely prevented the unexpected login to the remote management interface.
Default passwords are often easy to guess or publicly available, and attackers can use them to gain unauthorized access to devices and systems. Changing the default password to a strong and unique one reduces the risk of brute-force attacks and credential theft. Using least privilege, assigning individual user IDs, and reviewing logs more frequently are also good security practices, but they are not as effective as changing the default password in preventing the unexpected login. References: CompTIA Security+ Study Guide: Exam SY0-701, 9th Edition, page 116; Local Admin Accounts - Security Risks and Best Practices (Part 1)