Not saying it’s correct, but that’s the hypothesis.
I also think comparing human level of consciousness to animal level of consciousness is a hard position to defend.
Anyway I guess you're missing the original point. What it theorizes is that some mushroom compounds might have had effect on our ancestors brains and helped them develop to what we are now, over long periods of time. A bit like agriculture or writing had a huge impact on our societies, but it's not a on/off switch, it's a very long gradual process.
I don't know if there is a lot of evidence supporting it, but it's not news that some drugs can temporarily or permanently reshape parts of our brains.
It happens sometimes—feral children who are neglected or abandoned in various ways.
I’m not sure if that person would be more conscious than a dolphin, or a bear.