What does this book want to tell us? That SO2 doesn't exist in liquid or solid form because it is a discrete molecule?
What you can say is that the bond angles in SO2 and SeO2 are about 120 deg in gas phase and in solid SeO2 between 90 and 100 degree. Would be much more honest than speculating about some hypothetical hybridization which is not observable.
In case of SeO2 (solid) assuming no hybridization at all would probably describe the molecule even better.
Get a better book.