You are correct, the units in steps 9 and 10 are different. Steps 1-9 are part of an original iFixit tear-down, steps 10-15 are my user-created guide which iFixit staff have merged with their own.
There may be some variation between units, if your original disc drive didn't have a heat shield then I wouldn't worry. It doesn't appear that the unit in steps 1-9 from iFixit had one either. Thanks for the feedback, I'm glad the guide helped you fix your issue.