Surovell is known for publishing against alleged pre-Clovis sites, he does have a bias. But that is fine, you can be a long-term archaeologist and have an opinion, and there is a lot of sensationalism around pre-Clovis that needs to be criticized from somewhere.
I think Surovell is stretching things when he states the 11-thousand-year-old ash layer is "below" the site, in fact as you can see from the diagram and reading the paper, it is simply "absent". He qualifies it as "stratigraphically below" sometimes, which is accurate, but that depends on the stratigraphy he proposes, which is an interpretation.
It would be more accurate to state that the 11kyo ash layer in his stratigraphy predates the cutting of the river channel in which the site is found. The ash was deposited on a boggy peaty wetland (evident from the photos) and the river channel would have drained the wetland if it existed before then. They are going to be fighting about this for years.
Far more persuasive is the identification of a source of old bones and old wood upstream of the site that could have washed down and contaminated it or (though he doesn't say) could have served as a source of fuel and tools for the site's occupants. You can burn old wood, I have experimented with bits of wood eroding out of a bluff around here that has also produced mastodon tusks and it burns just fine if you dry it out. And a several-thousand-year-old gomphothere bone that just washed up on your little beach might make a good digging stick or whatever.
It is harder to explain the chewed seaweed balls or securely dated potatoes (though these are native to the Andes) but these samples apparently disappeared in a fire which is awfully convenient.
