Short answer: Generally you can shift just about any riff up or down 5 frets, switching strings and play the same melody. You found the correct note (pitch) which is the primary objective.
Sounds like the only thing you missed are Justin's notes from the lesson page:
There are two parts to these exercises.
Part A: Figure out the notes I'm playing - anywhere on the neck. Don't try and base it on a scale shape or worry about what it is, just try and find the notes. If I'm doing something like this I'd be starting around the 5th fret because it's kinda central, but it really doesn't matter - just don't use open position.
Part B: Work out WHERE I am playing... Everything I am playing is based around Minor Pentatonic Pattern 1, I am using other notes too, but as in the previous exercises it based around that basic Box 1. It's just a shape remember... you should be well familiar with it by now!!
So the "rules" of the exercise are why the answers are what the answers are - he was using Minor Pentatonic Pattern 1. But in the real world you very well may want to play the "riff" in a different place on the neck - in one of the other patterns.