Maybe Luke gave his green sabre to Ben Solo, who later modified it to be his red cross blade one. Either that, or the artists are simply using a single model for the light sabre.
That doesn't really track. Finding the crystal "meant" for them and building their own lightsaber is a key part of becoming a Jedi. It's not just a piece of technology, it's both a reflection and an extension of the person who made it. That Kylo's is cracked and *barely* stable is not an arbitrary thing.
More likely is that Luke cast his aside when he went into exile because he felt like he had no business claiming to be a Jedi anymore.
That or he still has it and for whatever reason they're not showing it in the promotional material yet.