I'm not sure if I should really count this as a movie, episode or special. I don't want to count this as cannon, I don't want the events of this episode to have happened. I am not a fan of Bardock, even in his "good" specials. Anytime they try to incorporate some sort of larger prophecy into the story. When they make it seem like it was destiny for Goku to become a super saiyan and defeat Frieza, it lessens both the characters and the story.
How did Bardock survive being exploded along with his planet? How did the events of this movie happen? Never explained. Just make up your own explanation. I'm going to say that the whole thing is either a bad dream Gohan is having, or because Bardock was such a brilliant scientist he managed to time travel. I don't know, it is still more of an explanation than this episode will offer.
Side note, the animation is too glossy. Everyone has too thick of outlines and it feels like it was made on the cheap. It makes the whole thing unappealing to watch.
As a bonus you find for collecting all items in a Tenkaichi video game, this episode is fine. But as a Dragon Ball episode, piece of continuity or even just as a narrative 3-act structure it fails.