Read the comic here.
I thought for sure I had left Buzz in the background in previous strips - but I guess he was cropped out. Whoops.
Oh well. Having Buzz lying around my workbench is pretty believable, even if it wasn't clearly established before hand.
And, no, Buzz isn't moving under his own power - Only Luka, Scotch and Donut have self-mobility in the Author-verse. Everything else....is just LEGO.