While Glosa definitely does seem to take a lot of influence from English, it's grammar isn't quite so indistinguishable from English's as to be an obvious relex.
It avoids classic relex mistakes like including do-support, and while its tense-aspect system doesn't do anything too wild for English speakers, it uses a variety of particles rather than English's auxiliary-based periphrastic tenses. It's also noteworthy that it lacks plurals, a decidedly un-English-like feature. Both these features were likely inspired by Mandarin Chinese.
Glosa also has an article that is unspecified for definiteness, using u(n) for both "the" and "a(n)", which is a departure from its major influences -- English, which has distinct definite and indefinite articles; Mandarin Chinese, which doesn't have any such articles; and Esperanto, which possesses one explicitly definite article. However, this article's syntactic behavior does not seem notably different from the English or Esperanto articles, so it's not thinking too far outside the box there.
You could definitely argue that Glosa's departures from English are pretty small, and that it's thus still quite relex-y in spirit. It's certainly closer to normal English grammatically than Interglossa, which is reportedly based on Simple English. So it really depends exactly how far you think a conlang must depart from English grammatically to "count" as not being a relex.
