Bond Angles of Hypofluorous Acid - Gas and Solid Phases
It is due to hydrogen bonding in the solid but not gas phase, in analogy to what occurs for the water bond angle.

From a VSPER point of view, the oxygen atom of one molecule would form a hydrogen bond with the hydrogen of another molecule, decreasing the repulsion of the lone pairs to be closer to that of the covalently bonded pairs, so the geometry would be closer to tetraherdral in the solid phase than in the gas phase.