RFC 20 shows "@" defined as "commercial at" in 1969. https://www.rfc-editor.org/rfc/rfc20.html . That was two years before Tomlinson used it for email addressing.

EDIT: "Creation of Computer Input in an Expanded Character Set" at https://ejournals.bc.edu/index.php/ital/article/download/292... from 1968, p112, describes it simply as "at".

EDIT #2: "TRANSLATION FROM MONOTYPE TAPE TO GRADE 2 BRAILLE" at p83 of https://archive.org/details/researchbulletin05lesl/page/82/m... from 1964 describes that symbol as the '"at" sign'.

I think that is early enough to say that email did not influence the "at" meaning but rather the other way around.