I can understand how sightings can be misinterpreted, especially when the witness is not expecting to see a big cat and has probably never seen a big cat at distance.
A similar thing happened at my parents' place. My brother walked out the side door and saw a mountain lion. His first impression was "damn thats a big cat!". The troubling part was how it nonchalantly stood up, and just walked away showing no fear or surprise.
There had never been a report of a mountain lion sighting in our area so naturally everyone was dubious, until the DOW caught it and her cub.
I have often thought that a tiger or leopard could make a pretty good living here in Colorado with the healthy populations of elk...and dogs...and people...