I remember the B-1 doing somehting similar at Boscombe Down about 20 years ago - a sedate wings unswept display then it disappeared as something else claimed the audience's attention, stage centre.
Was that it?
Somewhere out over Dorset a small brown cloud appeared which grew rapidly larger and proved to be a B-1 shaped exhaust trail - at something close to Mach 1 it pitched up into a very steep climb, aileron rolled once and punched a hole through the light alto stratus!