Actually, it is a Turing machine built using Lego. The part built using just Lego bricks however isn't a universal Turing machine. I don't see a claim anywhere that it's a UTM, just that it's a TM, which it clearly is.

BTW: The site links to the code running on the brick, which is a very simple parser for a basic TM language which interprets programs written in that language. So even though the "universal" part isn't done using basic bricks, it actually is a UTM.