This is not new, it was fist postulated in 1991 and proven in 2007.
This is why people who are quadriplegic don't need heart stimulation even if they need mechanical aided breathing, and why people with severe brain damage in a coma still have heart functionality.
The heart neurological complex (it is not an actual brain) is a evolved survival mechanism, it is remarkable but not miraculous and it certainly does not think in the same way the brain proper does and certainly gives no credence to the ancient Greek idea that the heart not the head is the seat of all reason.

It’s a fascinating article, but I kept looking for links to the scientific studies mentioned. I came across this by googling:

[nature.com]

[heartmath.org]

There are a lot of claims online about this subject, with statements like “research shows”, but no links to any real studies.

It makes sense that an organism’s entire nervous system be considered a unified whole. It’s all connected.

See no reason why not. The idea has millenia of thinkers considering it.