Dogs aren't all the same, even of the same breed, humans aren't all the same either...so why would you think all snakes would act the same? And he cannot tell
you how people before you have treated him, can he? or what happened on the way to your house? He has every reason to be afraid, & it takes as long as it takes
for him to mellow out. Nearly all do, but some of that depends on their human's skill & empathy too.