Infrared systems display differences in thermal radiation rather than a natural-colour view of the scene. A bright or dark patch can represent a real warm object, a cold object, exhaust, cloud structure, reflected radiation, a distant target blurred by the optics, or other contrast that the sensor can lock onto without revealing a clean physical silhouette.
An auto-track box is therefore evidence that the tracking algorithm found a sufficiently stable feature to follow. It is not, on its own, evidence that the feature was a solid craft or that its apparent movement across the display equals its true movement through three-dimensional space.
That distinction is where some retellings of PR103 run ahead of the primary source. Claims that PR103 shows “multiple UAP expanding and contracting,” for example, go beyond the primary wording. AARO describes an “area of contrast” held by the sensor and auto-tracker; its public caption does not identify multiple craft, expansion/contraction as physical behaviour, or any anomalous performance.