What does edgar allan poe mean by the use of the word sinister to describe the physician in the fall of the house of usher?

I believe the correct answer is hiding an important secret.
Although sinister does mean evil, or intending harm, I believe that Poe didn't use that word his with that meaning. This is the excerpt of when he met the man on the staircase:
"His countenance, I thought, wore a mingled expression of low cunning and perplexity. He accosted me with trepidation and passed on."
There is no evil feelings here - the narrator can only see that his host is afraid because of something, and he doesn't yet know why.

The details that best show evidence of tribal traditions are, "never in the history of his people had a man married a woman who spoke a different tongue” and "it has never been heard," was the verdict of an old man speaking a few weeks later.