I presume the subject must've been in pretty bad shape in terms of health, to assume the inherent risk of brain surgery at the micron scale. Best wishes to them, and I hope humanity can benefit from knowledge gathered with this breakthrough.
"Have quadriplegia (limited function in all 4 limbs) due to spinal cord injury or amyotrophic lateral sclerosis (ALS) and are at least 1-year post-injury (without improvement)"
They need to thread the needle of a condition so advanced that a brain link device would potentially restore a basic essential of life but also not so advanced that the patient can no longer give consent.
You can see the patient criteria they selected here: https://neuralink.com/pdfs/PRIME-Study-Brochure.pdf