> Not sure how someone is meant to parse that

Someone is meant to use context and understand that when the context clearly refers to someone who is well known to be a member of the board of directors, 'advisory board member' means that they are a board member in an advisory role, aka a nonexec.

That assumes that someone is familiar with the structure and makeup of boards of directors. It's a bit rude to participate in a conversation if you're not familiar with the subject matter and the meaning of words-in-context as you just waste peoples time making them elaborate.