Christopher Tolkien never commented on anything George R R Martin had said or written
While it is always difficult to prove a negative, Christopher Tolkien was a relatively quiet figure, especially in the last few decades of his life when George R R Martin made these statements.
Christopher's most public comments on works of Tolkien Criticism can be found in his History of Middle-earth series, which was published between 1983 and 1996.
In Chapter 7 of his book The Road to Middle-earth Professor T. A. Shippey accepts that this is so ...
In The Complete Guide to Middle-earth Robert Foster says ...
Professor Randel Helms, in Tolkien and the Silmarils (p. 93), has stated ...
And in an article entitled ‘The Text of The Hobbit: Putting Tolkien’s Notes in Order’ (English Studies in Canada, VII, 2, Summer 1981) Constance B. Hieatt concludes ...
The Book of Lost Tales Part One - "Foreword"
Barbara Strachey (Journeys of Frodo, maps 15-16) shows very unambiguously the ravine of Rivendell as the ravine of the tributary stream, Elrond's house being some mile and a half from its confluence with the Loudwater; while Karen Fonstad (The Atlas of Middle-earth, pp. 80, 101, etc.) likewise places Rivendell on the southerly stream - calling it (p. 127) the Bruinen.
The Return of the Shadow - Chapter XI - "From Weathertop to the Ford" - note
The last of these books came out in 1996, the same year as the first A Song of Ice and Fire book, and eighteen years before George R R Martin's tax policy line.
None of Christopher Tolkien's publications since then had this type of commentary on other works, and he did very few public appearances and only one press interview.
He continued to review and comment on such things through private correspondence (see his c.2006 remarks here on Douglas Charles Kane's Arda Reconstructed) while still alive, and it is possible that he'd seen and/or privately commented on George R.R. Martin, but he never did so publicly.