The Gospel of Thomas consists mostly of sayings, and it explicitly claims to be a Gospel in its first sentence. So that's pretty good evidence that something like Q would have been thought of as a gospel around the time when Thomas was written (which is sometime between the mid 1st and mid 2nd century, we don't know).
On the other hand, we don't know when "gospel" was first used as a name of a genre or writing. One theory is that it was first used to refer to a genre of writing in Mark 1:1. So it might be anachronistic to refer to Q as a gospel, since the genre may not have yet existed.