Youtube sensationlist bs. Fortunately there’s the paper link, so I went and looked, and here’s what they found (reformatted for readability)

30 groups with indeterminable morphotaxa numbers (‘spp’) were also included. These included

• groups of small individuals that swarm (e.g. Amphipoda and Mysida),
• groups with small indeterminable body sizes (e.g., Annelida, munnopsid Isopoda, Ophiuroidea, elasipodid Holothuroidea),
• individuals of groups that were often drifting too far from the camera to confidently identify (e.g., Appendicularia, Narcomedusae, Trachymedusae and Ctenophora) and
• other groups that are notoriously difficult to identify from images (e.g., Monothalamea).

It’s not “wild unknown deep sea creature”, it’s “we didn’t get a good enough picture to say what species this annelid is”.