Mindspawn is referring to the agreement of C-14 dating with tree rings. His proposal is that scientists are mistakenly identifying some rainfall induced tree rings with annual rings
Mindspawn's original objection to C-14 as a reliable dating method was that they leveraged what he considers unreliable ancillary calibration methods; i.e. tree rings, lake varves, etc.
Coyote responded by saying: Ok, if you have issue with those calibration methods, let us remove them and focus on the C-14 dating mechanism
itself. He then produced a graph showing C-14 decay rates over a particular timeframe, representing the half life decay of the isotope. Mindspawn responded by going back to the tree rings and lake varves.
From my understanding, Coyote performed a concession by ignoring those things which Mindspawn had issue with and focused solely on just C-14 itself. By doing so, he eliminated the original points that Mindspawn did not agree with. In turn, Mindspawn simply ignored the graph, stated that he didn't agree with the output displayed and claimed it was 'circular reasoning'. Which is false. The graph is the result of experimentation. It was evidence leading to a conclusion. Circular reasoning is coming to your conclusion first and then finding evidence to support it. You know, like assuming the bible is the word of god and infallible and then cherry picking evidence to support that claim while ignoring evidence to counter that claim.
Edited by Diomedes, : Fixed minor typos and grammar errors.