"Treemap" is the most common name in English for this chart type. The reason it is called this way is that it originally was used to show hierarchies; tree structures.
When we introduced this chart for version 7, we considered calling it "Treemap", but chose to call it "Block chart" instead. Partly because "Treemap" is poor name (from a descriptive point), partly because the chart often is used for structures that are not tree-like.
For Qlik Sense we have chosen to call it "Treemap", since this is the accepted name in English, and we wanted to be conform with the standard terminology. However, this change does not necessarily mean that translations into other languages should change.
I know that Treemap is actually the accepted, most common, standard name, but in my language this has been poorly translated as "Mapa de árbol" or alternatively "Diagrama de árbol", two terms that mislead the user as they can be easily confused with other kinds of visualizations that are very common, so I have decided to stick to the old name which has worked very well in the Spanish market and is so clear and descriptive. We prefer to keep our identity with the Block Chart if you don't mind!