The original Dragon Ball does depict some overt sexual content, although there's less of it in subsequent series. Master Roshi would often bluster over nude women while reading pornography. However, these scenes are censored when shown on television. There are "comedic" instances of sexual harassment with characters peeping on and sexually harassing girls like Bulma, and there is a fair bit of non-sexualized (and often censored) male nudity following Goku and Gohan's Great Ape transformations. Even at the franchise's most objectionable moments, however, no sex is shown on-screen, so describing this PG-13 series as "pornography" is a huge leap.
It's unclear if Miller has actually seen Dragon Ball, Dragon Ball Z, Dragon Ball GT or Dragon Ball Super. It is possible that Miller found a doujinshi hentai online and confused it for the real thing, but this remains uncertain. Any accusation of Dragon Ball Z being pornography is completely unfounded and divorced from Dragon Ball Z's nature as an action anime.