It is seldom if ever that I'm a defender of TSA or DHS, but in this particular instance it is likely that they either had to issue this directive or face having US aircraft banned from Russia for the duration of the Olympics. I'd blame the Russians for this more than I'd blame the TSA/DHS. My $.02 FWIW.
Would Putin really ban US and European flights to Russia during the duration of the Olympics over carry-on luggage restrictions? They already have a sort of PR disaster so far about these Olympics.