I think they are talking about his previous stint as a linguist. Before
he became a leftist superstar peddling media conspiracy theories, he
did make significant contributions to formal linguistic. Whether it
had enough impact to make him a top scientist though, is itself as much
of a contested question as Time's misguided attempt at canonizing a
bunch of pop thinkers. What really made me cringe though was the
art/entertainment category. Picasso, Stravinsky, Bart Simpson and Oprah
Winfrey. Huh?
Funny you mentioned McLuhan because a few days ago the McLuhanites here
hatched a press release onto the wire protesting Time's exclusion of
McLuhan from this pageant. The McLuhanites are sort of an amusing
endangered species here in Toronto because some of the more zealous ones
suffer from self-delusion about the importance of McLuhan and think they
hold the secret to an ignored prophet. The truth is his entire body of
writings consists of a few ideas ripped off from anthropology, which he
riffed on ad nauseum until everyone ignored him.