All architecture is design but not all design is architecture. Architecture represents the significant design decisions that shape a system, where significant is measured by cost of change.
One interpretation I can make of this quote is that it seems to be an inherent contradiction in aiming for agility in the design decisions that constitutes the architecture. Architecture is those decision that you don't want to change since it is costly to do so (in $$$, man hours or lead-time). But this is not the same as making those decisions up-front.
Maybe a lean approach is what benefits agile development the most:
...an architect should make as few decisions as possible, deferring the rest until later in the lifecycle.Tyree and Akermann in IEEE Software 22(2), 2005, pp. 19-27.
SEI has a webinar 22 April about Agile Development & Software Architecture. Maybe that can shed some more lights on how to reconcile architecture and agility. To bad they are broadcasting it at such an awkward time for us in Europe.