OK, suppose:
70% of people ticked 'at home' and one of the other three boxes,
20% just ticked 'at home'
10% just ticked one of the other boxes.
... i.e. 80% of people used their tablet away from home. That completely contradicts your position but could produce exactly the same chart.
Of course, the chart doesn't give enough information to actually support that position, any more than it supports yours, although it is pretty plausible that most people with a tablet would use it at home, regardless of where else they used it.
...and in any case none of this provides any evidence of the proportion of time spent using the tablets in each place ('use at home' could be 10 minutes on Plants vs Zombies of an evening after spending 8 hours iPadding your way around coffee shops and and public libraries), what importance they placed on each use, and whether size and weight was a factor in their home use.
As I said, maybe the chart is valid in its original context - although publishing a chart with a claim in its title and no specifics as to what it actually shows is a bad idea, but I went through 3 layers of websites that had cherry picked it to mean what they wanted it to mean, and never found the original source.