Their wording is really stupid but you did it the opposite way of what they asked. You should have chosen "Child/gran-child". If you read the question again and it's explanation you will know what I mean. Also, when you select that ONLY then you are provided with Super Visa option on next page and in all other cases you will see TRV on next page.
Now, I don't think this is really important because the answers to questionnaire is NOT submitted and main application form IMM5727 does has an option for selecting Super Visa on the form which will tell the VO this is for Super Visa but they might get confused as the application might come marked for TRV and I think that is why some people complain here that they got TRV instead of Super Visa.
The most important point here is to get the Visa and if you get rejected Super Visa because you don't have enough options to submit support documents then it's really stupid of the programmers to do this.
I also hear a lot that Super Visa is all dependent on the child/grand-child but then I hear people submitting all sorts of paper documents so if an officer is used to receiving all those paper documents they will not see the online document favorably even if the user followed what was rightly presented to them.