This is obviously an excellent report. Once again it is the Giant Sloth. In this case the creature chose to scare everyone away. The actual movement does suggest that it was not projecting an image as is plausible in other cases.
Most likely it wanted them out of its hunting territory.
Once again this creature neither gives chase or rushes to escape which strongly suggests that bipedal motion is poor. It relies on the upright position to scare you and set you off in a mad run. From there it has the option of dropping to all fours and giving chase up through the trees if necessary.
This is one scary carnivore.