It is an intriguing object, I see from the description you give that it is made of bronze, is about 5cm in length, and is dated to the 6th to 7th century AD.
I would suggest that, if this piece dates to the 6th or 7th century, it is too early for chess. The parallel with the Lewis Chessmen is unfounded; they are from the 12th century, much later. Chess didn’t reach England till at least the 10th century, if not the 11th.
Is it a gaming piece, then (as your article calls it)? I don’t personally know of a similar gaming piece of this date. The main games at this time were an early version of backgammon, derived from the Roman game duodecim scripta, and the game of hnefatafl.
The backgammon-type game may have used counters, such as the bone counter found at Lyminge in Kent a few years ago, from Taplow in Buckinghamshire, or from Sutton Hoo.
King goes to war
Hnefatafl is a possibility. It was a war game, with the king in the middle of the board, with his army around him, and at the edge of the board the other army surrounding them.
Generally the only figurative piece is the king, and the soldiers of the two armies are typically represented by plain pieces.
My opinion is that, on present evidence, if the horseman is dated to the 6th to 7th century, he is probably not a gaming piece.
There is no game of that date that is known to have had one. Also, 5cm is quite big for a square on a gaming board. I would suggest he’s either a model or possibly a toy.