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The one capture in this set that carries its own clock time, 21:17:57 on 12 August, the peak night. The star trails here are much shorter than in the other frames, so the streak stands out as several times longer than any trail around it.
Placeholder - the classification reasoning is still to be written. Length relative to the star trails is the observation worth keeping: a fixed star can only draw a track as long as the stack allows, so anything markedly longer moved independently of the sky. The recorded time is early in the evening and the crop alone does not establish how dark the sky was, nor whether that time is BST or UTC.