He's thinking of creativity as a formula, or something that has steps, that's sapped the fun away from it. It's one of my problems with many guides on drawing, or writing, or anything else - people treat them as strict step by step instructions, rather than starting points or something to fall back on.
Do the 3 act structure if you want to, or if it makes sense for your story, but don't be afraid to completely ignore it and do your own thing, and so forth.