There is no doubt, however, that at least under current law, he would be considered a terrorist. Here is a definition of terrorism in U.S. law (22 USC 2656f(d)f(2)) (there are others as well but similar):

the term “terrorism” means premeditated, politically motivated violence perpetrated against non-combatant targets by subnational groups or clandestine agents

The Weather Underground was a subnational group; exploding bombs is an act of violence; government offices are non-combatant targets (the Weather Underground also bombed banks); and the use of violence had the political goal of ending the Vietnam War. "Screaming response" or no, this was terrorism.

Under current law, Ayers was a terrorist. This definition is not idiosyncratic; similar definitions can be found in the laws of foreign countries and in international treaties. Ayers seems to think he ought to be excused for violence because his motives were good, but that is the excuse that terrorists always offer—that their political goals justify their use of violence—and naturally the legal definition could not permit such a defense without subverting itself, or turning every terrorism trial into a debate about whether the political ends of the defendants are "good" or "bad" from a moral or political perspective.