What is "a little armchair psychology"?

I’ve been reading about "Calabar beans":

Its chemical composition, along with a little armchair psychology,
may explain why the plant had such different effects on the poor souls
facing a trial by ordeal. A person who knew they were innocent might
chew the bean quickly and swallow it with pride, ingesting a quick dose
that would cause them to vomit before the bean could do more damage.
A guilty party, dreading death, might take tiny, slow bites. Ironically,
this attempt to prolong their own life would only hasten their death by
delivering a gradual, well-digested dose of poison.

I feel confused for the meaning of "a little armchair psychology" in the above the sentence.

"Its chemical composition, along with a little armchair psychology,
may explain why the plant had such different effects on the poor souls
facing a trial by ordeal."

= Based on its chemical composition and a little general psychology, we may know
why the plant had such different effects on the poor souls facing a trial by ordeal.

I’m not sure what I think is right.
Could you explain what "a little armchair psychology" means more easily?