The term "dumbo" is a fairly recent way of referring to octopods that belong to the genus Grimpoteuthis, as their popularity increased with the internet exposure they’ve received. There are about fifteen species in this genus, and were formerly called "jelly heads" by researchers before the "dumbo" meme took over. An equally silly, as well as apt, name.
While most octopuses are bottom-dwelling, it is believed that Grimpoteuthis are mainly pelagic since most specimens have been caught or filmed swimming in open water, although in the video above we can see they are also fairly comfortable crawling along the sand as well. The big ears that give this animal its common name are actually fins. By using these fins, as well as jet propulsion supplied by the animal’s siphon (which is the "nose-like" protrusion in the very top image), it can swim suspended a few inches off the bottom as it searches for crabs and shrimp to eat. While some resources call this cephalopod "benthic" and other sites say it is "pelagic", I think a more appropriate term, given the behavior described above, is "benthopelagic".