It had an air tight door to the tunnel so I would say yes. An earthen berm around a tank to contain hazardous material in the event of a rupture is a containment. Just because it is not reinforced three foot thick concrete does not exclude it from being called a containment. This was built before 1960, remember that San Onofre unit one had a concrete containment as an after thought not part of it's original design and the Navy S1W prototype containment was a building designed to collapse on the prototype submarine hull inside (did not give me a warm fuzzy feeling as that was my prototype school).
okay, fifty years of use followed by failure only plays into the hands of those who demand the NRC does not consider certifying MPCs, and other ISFSI "containments" for longer than twenty years,...
as it is, the Tri Party agencies already had a commitment to assess the condition of waste disposal tunnels near the PUREX processing plant by September 2017, I reckon they have been assessed to be failures,....