I don't have a live account with IGindex, but I have just opened a demo account with them to take a look at your question.
What you have said is absolutely correct. If you are buying in at a lower price then it's a limit order if you are buying in at a higher price then it's a stop order. I have a page in my beginners guide with a bit more detail on orders
The order ticket chooses the type for you based on your direction(buy/sell) and order level. For example buying the FTSE at 5900 (current price 5888.8) is stop buy order, buying at 5800 is a limit buy order. Why you are then given the opportunity to change the order type is beyond me. If I set to buy the FTSE at 5900 it auto populates the type box to 'stop' . If I change it to 'Limit' with the same values I get an error when I try to submit the order. It does beg the question why give me the option to change the order type?
Anyway back to the question bigAl asked, as far as I can tell what you have done is correct.
Tony Loton has written a book all about the different order types called Stop Orders
you can order a copy from Amazon here
. It's less than a tenner ,delivered, and there's more in there than just details about the different order types, including more detail on how he made a 3000% return in 6 months.
I hope all this info helps.
May the markets be with you!
The Spread betting beginner