As an example, take Google's self-driving cars. Would you say the meat of their body of work theoretical? But would say the code they (Sebastian Thrun himself, and others involved in the project) write code that's not very practical, readable, maintainable or without tests? I would say what they do is theoretical work. And they write practical code for their theoretical work.
If you look at Udacity classes - I've watched Peter Norvig not Thrun's so I'll use that as a reference - Norvig places a lot of importance for tests, maintainability, readability and other practical things throughout his class. I would assume the code he writes (however little now, however much in the past) is very practical. Yet what he writes code for has a huge theoretical aspect to it. I'm saying one can have their body of work being theoretical by nature but that doesn't mean they don't write practical code.