The cool thing about being in 2023 is that you don't have to believe me. Winding up a Windows XP virtual machine with Visual Studio of your choice takes 15-20 minutes.
This was likely ASP.NET code. In the early days many folks just FTP'd their whole ASP.NET project folder to IIS, including the source code (e.g. .aspx.cs code behind etc) when you didn't need to. There was a lot of misunderstanding about how to deploy ASP.NET applications, many folks were still working with a Classic ASP mindset. I speak from experience as my company's .NET go to engineer and developer for a shared hosting company back in the day and having to explain to customers how to deploy their apps sans the source code.
No, it wasn't lol. I wish people would stop telling me what I very clearly remember. I did a report on this in high school - how C# programs (desktop programs) could have their source recovered under certain build conditions.
> how C# programs (desktop programs) could have their source recovered under certain build conditions.
Yes, using a tool such as .NET Reflector, but the source was never embedded in the compiled binaries, or anywhere else if you were competent with the toolchain.