It's also possible that they might think what they saw was Bigfoot, or a Sasquatch, or windigo, depending on precisely who saw it, for how long, and in what sort of situation.
Something big and furry glimpsed running through the bush? Wolf, wild horse, bear, moose, deer, caribou, someone wearing furs, the list goes on.
Something bipedal and furry? Possibly a bear, they do stand up on occasion, someone wearing furs, or one of several supernatural or mythological creatures.
I did find this mention on the Bigfoot wiki entry
Bigfoot wiki entry wrote:Some regional versions contained more nefarious creatures. The stiyaha or kwi-kwiyai were a nocturnal race that children were told not to say the names of lest the monsters hear and come to carry off a person—sometimes to be killed.[14] In 1847, Paul Kane reported stories by the native people about skoocooms: a race of cannibalistic wild men living on the peak of Mount St. Helens.[9] The skoocooms appear to have been regarded as supernatural, rather than natural.[9]
Less menacing versions such as the one recorded by Reverend Elkanah Walker exist. In 1840, Walker, a Protestant missionary, recorded stories of giants among the Native Americans living in Spokane, Washington. The Indians claimed that these giants lived on and around the peaks of nearby mountains and stole salmon from the fishermen's nets.[15]
If google and memory serves me well, Washington state and Montana are basically right next to one another, so it's probable that stories going around one would drift over into the other.
Though, I suppose it depends on exactly what kind of people we're talking about here, since all they might know about werewolves is a story or two heard while drinking around the campfire.
It's worth noting that silver wasn't seen as the werewolf remedy of choice, that only came into prominence after the Wolf Man film, though the silver=pure and good association had been around for a long, long time.
Also, forensic techniques of the time was most likely limited to "Bitten or clawed to death, probably bears or wolves." And it would take a rare person indeed to notice, or even think to check, that the bite patterns matched human teeth rather than wolf or bear teeth. Assuming your werewolves don't magically grow extra teeth to match what wolves are equipped with.
Probably, the most likely thing people would think if they saw a werewolf would be "evil spawn of the devil" or something, or possibly a nature spirit of some kind. It depends.
If you haven't already checked, I suggest reading up on the following.
Yenaldooshi(Skin-walkers).
Wendigo
If you haven't seen it already,
Ravenous seems to be just the thing you need. Cannibalism set in 1840 California.