Where is this from?


No. That is not legal.

I read that years ago in parts of central Europe moving a3 and h3 simultaneously was a common opening move, but it is not and never was a legal move.

No, the only legal move involving more than one piece of one color is castling. What you are describing sounds more like what street hustlers do: they make illegal moves by distracting you with talk, by "thinking" what move to play by moving their hands around and "accidentally" changing positions of some pieces... Some hustler could play 1. h3 clearly, and carefully move the a3 pawn at the same time, hoping you won't notice that - and it will be too late to complain a few moves in the game.

Back in the 1800s, masters often gave piece-odds to amateur players, so playing without a piece, usually a Queenside Rook or Knight. In some of these games, White would start with a3 already played, almost as compensation. This is why if you read game collections from the romantic era, you'll sometimes see the little annotation (with no Ra1, White pawn starting on a3) before the game starts.
The idea was, iirc, to deny Black the easy idea of e5, Nf6, waiting for the d-pawn to move and then playing Bb4+ and castling. This practice faded over the years, no doubt in part to master's playing odds-games much less frequently.