As illustrated in other blog posts (like http://bigblog.tanbin.com/2013/06/routed-events-learning-notes.html), a button click can be connected to (via xaml) a regular instance method in the xaml class (code behind), provided the method is an event handler. In this implementation, we are using a CLR event, not really routed event.
This simple design draws criticism such as tight coupling etc. There’s an alternative. Using commands, we can refactor to meet the same requirement. [[wpf succinctly]] has a simple example of this refactor.
Another book says — “In WPF and Silverlight, there are two ways to respond to user interaction: with events and with commands. Most controls will support both of these methods of interaction, but it seems more common for events to be exposed.“