The key is that code isn't running in a vacuum. It's operating on data (or controlling systems, etc). A smaller amount of code may be operating on the data in an inefficient manner, whereas a larger amount may be doing it more efficiently.
In the above talk, this contrast is very stark, because the "more code" version does some stuff and then does the exact thing the "less code" version does, yet is faster.
This kind of thing is common enough (albeit less stark than in the above example), that "less code is faster" is not a great "default" assumption to make.
The key is that code isn't running in a vacuum. It's operating on data (or controlling systems, etc). A smaller amount of code may be operating on the data in an inefficient manner, whereas a larger amount may be doing it more efficiently.
In the above talk, this contrast is very stark, because the "more code" version does some stuff and then does the exact thing the "less code" version does, yet is faster.
This kind of thing is common enough (albeit less stark than in the above example), that "less code is faster" is not a great "default" assumption to make.