A word artsy people use when they don't actually have an explanation or strong idea for what they did. Basically in this sense, conceptual can also mean "my bullshit"
Art Professor: So what are you interested in doing?
Art Student: I'm thinking about doing a film, but not narrative or documentary or performance piece. Conceptually it's abstract and, uh....It's just a very conceptual piece.
Art Professor: You have no idea what you're talking about, do you?
Art Student: No, no I don't.