The article doesn't once say cable TV never had ads; it only says the public had some perception that would be the case. In fact, it even talks about how cable channels were bringing in millions of dollars in ad revenues despite being very small markets at the time.

In reality, cable TV had ads from day one, decades before this article was published. Originally every cable TV station had ads, because they were just retransmissions of broadcast stations which ran ads. The first nation-wide cable TV station had ads, and many of the early cable-only channels (CNN, USA, others) had ads.