No, he probably did it just for fun, out of curiosity and to share something else than "hey look at my 976th scale model build!". But other people might be tempted to build and use it, for whatever reason.
I can already imagine the conversation when someone who painted his model using this DIY airbrush shows a build:
DIY airbrush guy: "Hi, look at my latest scale model build. It's a '69 Olds 420"
Other guy: "Nice! What airbrush did you use to paint the body?"
DIY airbrush guy: "I used a insert expensive airbrush model here."
Other guy: "Thanks. Really nice! See you."
DIY airbrush guy: "No, jk, actually I used this cheap DIY airbrush."
Other guy: "Oh! Now that you say it, I think yout paintjob turned out semi-optimal. Look at that... and this spot... and..."