Later, the same participants were scanned listening to a new story or imagining telling a story and the decoder was used to generate text from brain activity alone. About half the time, the text closely – and sometimes precisely – matched the intended meanings of the original words.

You left out the most important context about "half of the time". Guessing what you're thinking of by just looking at your brain activity with a 50% accuracy is a very very good achievement - it's not pulling it out of a 1 or 0 outcome like you're with your coin flip.

You can pretend that the AI is useless and you're the smartest boy in the class all you want, doesn't negate the accomplishments.