Only secondary to

Hi there. I have two questions about the following text from Art and Advertising by Joan Gibbons.

1. Does the green section imply "there is some kind of close relationship between this artwork and the language of advertising that this relationship also includes the medium of this artwork that is neon light (because neon lights are mainly used in advertisements)"?

2. Does "only secondary to the billboard" here mean "after billboards it is probably the most popular medium in advertising"?

Text:

Nauman follows Beckett not only in the way that he plays with the cliché, but also in the way that he inverts the meaning of words and plays them off against one another through slippage. As Vincent Labaume puts it: ‘It is as if Nauman begins by provoking a kind of faux pas, or Freudian slip, and then tries to correct it, to make up for and erase it as best he can.’ Here, Labaume is speaking of Neon Sign (1970), which places the phrases ‘none sing’ and ‘neon sign’ next to each other (NONE SING/NEON SIGN) and in which a simple shuffling around of the letters calls attention to the contingent nature of words and the ease with which small slips or shifts can alter the meaning of a word or even the whole sense of a phrase. Moreover, as is also the case with Holzer’s use of electronic signage, there is a sort of familial relationship with the language of advertising that can be stretched to incorporate the medium that carries the words. Here, the choice of neon as a preferred medium is of key importance, since neon lighting is perhaps only secondary to the billboard in its significance as a medium for outdoor advertising.