They appear to be reporting the most likely estimate. Normally, when a single value is reported, it is the median (50% cumulative probability). However, the probabilities are similar over wide ranges. You can use Doug McDonald's calculator to get an idea of what the distributions look like. Note that he uses transmission events (meioses), instead of generations. It is necessary to divide by 2 to convert to the latter. People should use 43 markers for Ancestry, since DYS19b and DYS464e and DS464f usually do not show up, and a mutation rate of .002.
http://www.dna-project.clan-donald-usa.org/tmrca.htmFTDNA provides guidelines based on TMRCA. Most people find them more useful than the actual numbers. They are in the FAQs.