The words belong to an art restorer’s jargon. To understand it fully, let’s begin with impasto, which is the strokes of thick paint where you can see peaks and valleys and brush strokes that all give the painting a tactile 3d surface.
Since this is in essence an artist’s signature touches to a painting, art restorers are very keen on retaining this authentic quality at all costs.
Crushed impasto is thus unskillful restoration. E.g through re-lining of a painting the heat generated can melt the paint and flatten the impasto effects. It is a sad side-effect to treatment, that could devalue a painting considerably.