All of the climatological and dendrochonological stuff I've dealt with has been much later, but some initial observations:

• I assume the reproduction (ie. the number of comparison samples of trees) is extremely low; usually a reproduction of fewer than 20 (?) is not considered to be particularly accurate, and I would be surprised if we have that here.

• If you're looking for evidence of a sudden cooling, you need to layer your data - dendro + ice cores, at the very least. Ice is extremely unreliable that far back, even with new methods.

• If there was a volcanically-forced climate event, we would see it elsewhere in the northern hemisphere, and being able to find similar evidence in Asia and the Americas would be vital.

• Finding a fluctuation in ^14 C that perfectly dates the thing to the time you want it seems really very convenient indeed.

Sooo, tl;dr: highly skeptical.