I think the intent was that when we first see just the bridge entering the shot, we are to assume it's just another Star Destroyer, but the entire sequence reveals it's actually the Executor.

Shot 1: What we think is a Star Destroyer bridge moves right to left obscuring the other Star Destroyers in the shot. (A possible hint at the scale of what's to come.)

Shot 2: A giant shadow moves in the same direction (right to left) covering a single Star Destroyer.

Shot 3: A closer shot of the same Star Destroyer being covered by the right to left moving shadow.

Shot 4: The camera looks up from behind the now fully shadowed Star Destroyer from the previous shots to reveal what created the shadow over it. At this point we are seeing just a portion of the Executor which shows its scale.

Shot 5: A wide shot to reveal the entire Executor with the shadowed Star Destroyer from the previous shots still beneath it.

This build up to reveal the Executor was always clear to me since 1980.