according to the article the entire country was occupied,
The claim that it was "occupied" is wrong mainly because neither of Poland's enemies had enough soldiers to leave garrisons in every town and castle they captured (or which betrayed to their side - like nobility of Greater Poland at Ujscie or Lithuanian Radziwill family at Kiejdany). And also because they never managed to control every single major urban center or stronghold (some of large, well-defended cities and fortresses remained in Polish hands all the time).
But wartime operations ravaged nearly entire country.
The map which can be found on English wikipedia claims that it describes "area occupied by Sweden and by Russia" - in fact these are areas of the farthest extent of advance / operation of Swedish and Russian forces (and they are described like this in PPWK's "Historical Atlas of Poland"). Not all of those areas were controlled / occupied by enemy forces at the same time, but all of them were ravaged by the invaders at least once during the war.
Also Transylvanian forces of prince George II Rakoczi devastated enormous area of land in 1657. They marched as far to the north as the Narew river. Later they were finally defeated by Polish forces in Ukraine in two major battles, but before that they managed to ravage huge territory.
I did not refer to that as something which should discredit the view that the losses were akin to a genocide- if anything it gives such a claim more credence.
Common practice of Swedish forces was to exterminate population of towns and villages which were owned by people who did not support the Swedish king. So we can call it a genocide because the definition of a genocide includes also murders motivated by political factors (not only ethnic and religious factors).
If some magnate at the beginning betrayed to the Swedish side and later changed his mind (i.e. started to resist the Swedish invaders), then his property was being immediately ravaged by Swedish forces and his subjects massacres. Many private towns were destroyed this way.
But also towns which were Royal Property of the Polish king were ravaged mercilessly. Some of them vanished completely.
Those crimes were motivated by desire to plunder ($$$) and by desire to supress political opposition via destroying their real estate.
Of course Swedish crimes were partially also motivated by religious factors - they were Lutherans in a mostly Catholic-Jewish country.
It should be noted that Sweden in 1650s was a country of very poor people compared to inhabitants of Poland-Lithuania. An average Swedish peasant, who was conscripted to the Swedish army which invaded Poland in 1655, could see "wonders" that were unusual and rare in his home country. This contributed to their brutality.
The same extraordinary savagery was typical for Swedish forces during the Thirty Years War, when they mercilessly plundered German states. Brutality in general was typical for all wars and all armies of the 17th century Europe - but the Swedish army was known for its extraordinary savagery already at that time, when all armies were brutal.
It should be noted that also Polish forces contributed to destructions - especially in Greater Poland, which was a region that betrayed in 1655 and supported the Swedish king early in the war. In later stages of the war Polish forces under Stefan Czarniecki took revenge on traitors from 1655.
Stefan Czarniecki tried to discourage his soldiers from taking revenge on local population of this land which betrayed. Czarniecki even personally carried out executions of insubordinate soldiers who plundered real estate in Greater Poland (all caught red-handed were being sentenced to death).
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Edit:
I made a map showing military operations of main forces of the invaders in period 1654 - 1657 (these are movements of main forces only, I did not include operation of minor units which were assigned with various tasks, like for example the siege of Jasna Gora / Czestochowa):
http://postimg.org/image/b56iokm1j/full/
