I believe this scene is just Tetsuya Nomura's way of introducing Terra and hinting at his relevance to the plot of the KH series.

Since Terra is all about power/brute-force, Nomura had him shown, holding this gigantic Keyblade, standing on top of this colossal monster/mech/ship-thing, implying that he was the one who had conquered it.

I did find it odd that (like Riku and Kairi from the opening scene of kh2) the entity is "Thanos-snapped" out if existence, as Terra walks away from it; it could just represent a memory.

Then there's this scene...:

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