Betta Fish: Is this normal Betta behavior or is there something wrong?

I got this black samurai betta a week ago and he's eating normally and pretty curious and active. Recently I have seen this behaviour where is "beats himself/splashes himself into the sand"

Is this normal?

My tank is 25cm x 25cm 4 gallon tank with all parameters normal. No heater. Filter and airstone set on light.

Grey sansibar sand, limestone rock, driftwood which is releasing tannis and a plant.

Please advice.