I presume base drag was the launch ramp rubbing on the cover?
No, "base drag" in a rocket is the drag caused by the flat base of the rocket, as air rushes past, it creates an area of low pressure, with recirculation. On atmospheric rockets, it's typically a very significant factor in the performance, maybe 20-30% of the total drag*.
I am skeptical of that explanation, from Truax, because the cover blew off before it even got to the end of the ramp. Maybe, the entrained air caused enough local pressure drop to cause a similar effect, but normally its a function of the rocket airspeed VS the base pressure rise from the exhaust, so you would expect it to be higher the faster it was going, not right off the pad. The rear closure clearly failed almost immediately, but it looked like it was just from acceleration, like they either got it WAY wrong on the load analysis, or, it wasn't properly latched (however they latched it). Of course, we all watched it live, and I and my rocket buddies knew *immediately* that it was going to have a problem.
Brett
*This is odd, base drag came up in another context (FAI) just the other day - base drag is the reason that it's extraordinarily difficult for US modelers to be successful in FAI spacemodeling. It's more-or-less rigged for the Eastern Europeans, primarily because they have access to engines with somewhat smaller diameters for a given impulse. These engines are about .4" in diameter and not available in the USA legally. Estes and Apogee mini-engines (available in the USA) are 1/2" diameter. This alone would make them uncompetitive because even 1/10" difference in the diameter is enough to cause the base drag to be much higher, crippling the performance - .196 square inches VS .126. There's a little more to it, but that would be enough.
How would you like to compete in a world championship with models you built, and shipped across to Romania, without having any way to test fly them first, or in fact, have never seen the engine you were going to use? They do pretty good, even with that sort of handicap.