According to Wikipedia (if you can't trust them, who can you trust?):
"When foraging, it [the manta ray] slowly swims around its prey, herding it into a tight "ball" and then speeds through the bunched organisms with a wide-open mouth"
To me personally, that sounds like true predation.
Arguably, defining the term "predator" is an almost metaphysical experience:
At one extreme you've got Dr. Walter H. Adey referring to herbivores as "predators on plants" and at the other you've got things like cougars and great white sharks that target specific prey individuals.
How about baleen whales - Humpbacks use sophisticated 'herding' techniques to concentrate their food while Bowheads and Rights presumably do not but both are eating a pretty specific animal based diet. Is one more of a predator that the other?
Further, what can be made of an isopod (often a cirolanid) that will attack a much larger fish, eat its fill, and then drop off (often without killing the fish); then repeat the sequence the next time it's feeling hungry? Is it necessary to kill something to be a predator?