refpoison appears to be returning the amount of poison the other bot has, rather than the number of poison commands it has. The wiki and in-game help both say "How many .strpoison commands do you have in your DNA? Returns the number to me".
With a bot species designed to stay at 500 poison, with one member of that species looking at another, the poison variables are:
refpoison: 500
mypoison: 12
poison: 500