Most of the marks are pretty clearly giant squid, but last I heard scientists were still unsure about others. Probably something very similar. It's not too surprising, really. What we know about giant squid is mostly from a very few dead ones that have washed up. The vast majority (assuming we can even judge prevalence from things like scars on sperm whales) are likely to settle on the bottom. There are a great many creatures both big and small that live and die down there with none ever reaching the surface intact enough to be recognized as a species we haven't seen before. Every single time they send a probe down there, they find new ones. Some day maybe they'll find one of the big ones that could explain those extra sperm-whale scars.