What was the topology of the seafloor where the artifacts were found? I'd bet the location was a former marshland, which would have been sheltered from direct wave action. Anyone who has ever seen a glass beach should be familiar with the grinding power of the ocean on seachore level items.
As for burial. The introduction of burial pits for trash didn't come about until humankind abandoned nomadic life and began building semipermanent settlements. There wasn't any reason to bury trash before this...it would have been a lot of effort simply to "clean up" a site that would be abandoned within a day or two anyway. When humans started building our first villages, we had to devise ways to dispose of hard trash. The first trash pits show up shortly thereafter.
The problem is, we're talking about the closing days of the Pleistocene here, so for the first part there were NO villages ANYWHERE on the planet. The first villages didn't start showing up until the Natufians began building primitive settlements in the Levant during the opening days of the Holocene. That's half a world away.
The other thing to consider is that North America wouldn't have been friendly territory for seagoing peoples during the last ice age. On the east coast, the permanent icepack started around modern day New York, and on the west it was right around Seattle. The winter ice packs extended down to Mexico on the west coast, and Virginia on the east. Most Mesolithic coastal cultures developed in areas were the sea acted as a moderator to the weather, preventing temperature extremes and permitting the development of fish based economies. That amount of sea ice surrounding North America would have completely precluded that type of development.