He mentioned this because minimizing the indentation level of method bodies is arguably more important to readability and maintainability than the number of return statements (assuming the return statements are exclusively at the beginning and end of methods). Enforcing a valid context and only then doing work is one of the tenants of confident coding. Because this method is so simple, it isn't really a good example. A better demonstration of why this is a useful strategy could probably be achieved by rewriting your check_entry method.

Here's the talk I usually link whenever this comes up: https://www.youtube.com/watch?v=T8J0j2xJFgQ