I think, what he meant is, that one could easily assume that they had contact with certain drugs, because they simply showed a certain lifestyle where it wasn't that unusual to take drugs. I mean, what Japanese think of that lifestyle I (and of course every other person who doesn't live in Japan or doesn't have experiences from there) cannot know, but since their appearance was similar to western bands, who indeed took drugs, one really could get this suspicion.
But that's then far away from claiming they really took drugs, in my opinion.