Strange pop-up during upgrade to XCode 13.2

During the process of updating Xcode from verison 13.1 to 13.2, I got a pop-up stating:

Existing software on your system loaded a system extension signed by "Oracle America, Inc." which will be incompatible with a future version of macOS. Contact the developer for support.

This seems wierd. Has anyone else experienced this? I can't find any recent results on Google.

If it was part of the XCode upgrade, then why doesn't it state that... and why is it talking about Oracle?

If it's not part of the upgrade... well... the only thing I can think of is that I had Oracle Virtual box installed a long time ago (uninstalled long ago also because it is apparently not compatible with Monterey)... but why would this popup be re-triggered by an XCode upgrade?

Oh, and most importantly, did someone just put a rootkit on my mac?

Anything that triggers a re-scan will popup this type of message; a system update, or in this case Xcode. Many similar messages were seen in Mojave, prior to the demise of 32-bit support. You're being warned the extension is end-of-life & will cease to work in a future update.

I can only guess that you didn't uninstall VirtualBox correctly - perhaps only throwing out the app itself.

OSXDaily has instructions on how to fully uninstall VirtualBox - both automatic & manual methods. See How to Uninstall VirtualBox on Mac
The general rule on uninstall is that if it needed an installer app to install it, it will need one to uninstall it, or risk leaving bits behind.
For future occasions, I'd perhaps suggest AppCleaner (Freeware).

I see no reason to believe this is any type of malware, merely an incomplete uninstall.