I think that the terminology here is a bit confusing. The article you linked to describes two ways of deploying managed code - either manually, or through a solution. But I think calling the manual deployment method "working with the object model" is misleading.
No matter which way you decide to deploy, your event receiver is going to be written in C# code, and therefore you will be using the server object model
In both cases, your code will be compiled into a .dll. It's just that with a solution deployment, the .dll will be packaged inside the WSP file, and SharePoint will automatically make sure the .dll is installed where it needs to be (which may be different places depending on if it is a Farm solution or a Sandbox solution). If you are doing a manual installation, you have no package, and you have to make sure the .dll is installed everywhere it needs to be.
But still, in both cases, you are writing managed server-side code that interacts with the server object model.