Sure, there are ways to "break" it. The point here is to demonstrate that if you try to intuitively go for manual "non-randomness", you won't be as random as you think, sometimes surprisingly off from ~50%.
Actually the quickest way I found to "break" it and hover at ~50% is to simply aim for the dead space between the "F" and "D" keys. If it was using non-adjacent keys like "F" and "J" instead it would be better for its purpose. "Q" and "P" might work even better since it would mostly force you to use 2 hands, making it much harder to score close to 50%.
You are onto something here. This reminds me of various hierarchies of logic(Bertrand Russell's arguments). To beat a person such as you, all it has to do is lie - and tell you at the end it has been lying all along.
Your premise "open the source code for this, run it in node, get the probability of guessing f or d, and then guess the one that's lower" goes straight against the explicit request to try to type randomly, everything that follows althoug may be correct doesn't apply here.
This is like showing someone an elaborate mirror, and saying, "See? My copy of you does exactly what you're doing to do! You don't have free will!"
All you have to do is put another mirror in the middle and show them that it doesn't work as they claim.