Honestly I think it’s more likely he ditched it because it wasn’t winning battles. There isn’t any indication he loved any of his Pokémon back in gen I, (Professor Oak explicitly says this is the reason you beat him.) and his entire endgame team is made up of tryhard mons with high BST. Radicate didn’t fit this mold, and it would be perfectly in character for him to just get frustrated and release it. I think the fact that his next fight after this being at a graveyard is coincidental, since he certainly doesn’t act like he’s mourning in dialogue.