Surprise surprise, the iPad’s split keyboard includes “invisible” keys.
When you click slightly to the right of the left hand side keyboard, the adjacent letter on the opposite side‘s keyboard is typed, vice versa.
Below is a diagram with the range and values of those zones.
Made to help those who don’t follow the standard keys-to-fingers, the extended touch zones have probably helped you a few times. And probably again now that you know about them!