The word "explain" works a bit like "know" (and perhaps "teach", I think). No, you don't "know" that the Earth is flat; you just mistakenly think so. (And no, you don't "teach" kids that the Earth is flat; you just mislead them.)

To say that Schmidt "explained" that artillery, tanks and armies are obsolete implies that that is true, which... At the very least, remains to be seen. The correct term would be something like "He further goes on to bloviate about how artillery, tanks and..."