`xdg-open` thinks I'm running WSL, and fails because I'm not?

When I try to open a pdf file with xdg-open file.pdf, I get the following error message:

jonas@jonas-thinkpad:~$ xdg-open file.pdf 
grep: /proc/sys/fs/binfmt_misc/WSLInterop: No such file or directory
WSL Interopability is disabled. Please enable it before using WSL.
grep: /proc/sys/fs/binfmt_misc/WSLInterop: No such file or directory
[error] WSL Interoperability is disabled. Please enable it before using WSL.
jonas@jonas-thinkpad:~$ /usr/bin/wslview: line 216: /mnt/c/Windows/System32/reg.exe: No such file or directory
/usr/bin/wslview: line 308: [: -ge: unary operator expected
[error] This protocol is not supported before version 1903.

For some reason it tries to do WSL shenannigans? As I don't use Windows, I really don't understand why this happens. xdg seems to be configured to open pdf files with okular:

jonas@jonas-thinkpad:~$ xdg-mime query default application/pdf
okularApplication_pdf.desktop

And this is what okularApplication_pdf.desktop looks like:

[Desktop Entry]
MimeType=application/pdf;application/x-gzpdf;application/x-bzpdf;application/x-wwf;
Terminal=false
Name=Okular
Name[ar]=اوكلار
Name[az]=Okular
--- omitted languages ---
Name[zh_TW]=文件檢視_Okular
GenericName=Document Viewer
GenericName[ar]=عارض المستندات
--- omitted languages ---
GenericName[zh_TW]=文件檢視器
Comment=Universal document viewer
Comment[ar]=عارض المستندات عالمي
--- omitted languages ---
Comment[zh_TW]=通用文件檢視器
Exec=okular %U
Icon=okular
Type=Application
InitialPreference=8
Categories=Qt;KDE;Graphics;Viewer;
X-KDE-Keywords=PDF, Portable Document Format
X-KDE-Keywords[ar]=PDF, Portable Document Format
--- omitted languages ---
X-KDE-Keywords[zh_TW]=PDF, Portable Document Format
NoDisplay=true

Looks totally fine to me. Any clue what is going on here?

As always, less than 5 minutes after asking the question I find the answer: For some mysterious reason, I had the package wslu installed. A simple

sudo apt remove wslu

resolved the error.