Outputting supertables within a matrix
I think your output is wrong. Looking at your code and explanation, {% for row in entry.hgroup %} should be: {% for row in block.hgroup %}

Same goes for {{ entry.heading }} This should be: {{ row.heading }}

Copy should be: {{ block.copy }}

Working with matrixes and Supertable's is hard in the beginning but you'll get the hang of it. 

When you loop over you {{ entry.about }} you loop using a variable named block. that should be used for every field you want to output that's in the matrix field. Same goes for SuperTable's only just one layer deeper.