I did a tiny amount of searching to verify this but came up empty handed. Guest additions (what I think you meant) is GPLv2, so it should be free for use.
It is presumably referring to “VirtualBox 6.1.32 Oracle VM VirtualBox Extension Pack”:
> Support for USB 2.0 and USB 3.0 devices, VirtualBox RDP, disk encryption, NVMe and PXE boot for Intel cards.
> The Extension Pack binaries are released under the VirtualBox Personal Use and Evaluation License (PUEL).
The vast majority including I, only ever used guest additions (GPL).
That would not surprise me. Back when we were considering virtualisers many years ago, the issue was one of the reasons² I recommended against vbox despite using it at home - it felt a bit too dark-patterny¹ for my tastes. We went with a VMWare tool instead.
[1] though I'm not sure the term “dark pattern” had been coined, or if it had it was in my vocab, at that point
[2] another being Oracles general behaviour at the time - this was after their purchase of Sun and therefore Virtual Box.