[2020] Bug? Or do I not know the rules? Dreadhorde Arcanist and Spikefield Hazard

I attacked with Dreadhorde Arcanist, targeting a Spikefield Hazard. I was then given the choice to cast the front side (deal 1 damage blah blah blah) or backside as a land. Curious, I clicked the land side to see what would happen, and the land entered tapped, as if I played it from my hand. Is this working correctly? My understanding was that I couldn’t cast an instant and play it as a land because you don’t “cast” lands.