This is not a standard app (or driver) method. When the app is first installed, installed() is run; when it is re-saved by hitting "Done," updated() is run (simply saving code will not cause either of these to run). Many people make a method called initialize() and call it from either or both of these (probably because much example code does the same--and presumably this code code does it because there are often things you want to do in both cases, so having such a method may be helpful), but this would explain why initialize() is not run on its own under any circumstance--it's just not special. 
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