weird pawn moves

i was playing a game with french defense and came accross a really weird engine suggestion in post game analysis. its a really weird pawn move hxg3 while g3 square is vacant. its no en passant as well. is it some other wierd rule i do not know. for reference i ve tried to recreate the same move and m sharing the notations below. i m playing through the app. [Event "Computer"] [Site ""] [Date "07-Oct-2017"] [White "khushmonster"] [Black "Comp"] [Result "*"] [SetUp "1"] [FEN "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1"] 1. e4 e5 2. Be2 Bc5 3. a3 Ne7 4. g4 O-O 5. hxg3 * Sent from my Android