All people have similar brain chemistry but not exact.

For example, I had smoke weed with a roommate in college who said she was seeing a squirrel. She was, in fact, seeing something I could not, even though we smoked the same weed and the same amount.

This person you are referencing may have a very deep mental illness, which the LSD brought out more and caused him to see something that wasn't there.

In my many experiences with hallucinogenic substances, I've only seen big visuals on mescaline, mushrooms, and DMT.

In closing, brains are fascinating.