In fact we know now that morale in the East End was decidedly shaky and close to panic. I've also seen a captured Luftwaffe training film held by the IWM, viewed on one of their huge Steenbeck flatbeds at the film archive and as far as I know never otherwise released. The film shows an approach along the ribbon of the Thames, with intermediate targets of Barking, Dagenham and the Royal Arsenal to right and left, but the destination point for the navigator and bomb aimer was Tower Bridge; once reached, the area all about was fair game.
The bombing density map below, for the period up to October 1941, declassified in 1971, tells a story that supports the IWM's training film. That in fact it wasn't the East End, but the West End that bore the brunt of the bombing. The Arsenal appears as a blank, bomb damage there being even too secret for 'Most Secret' classification.
Until further information is found we can only speculate on the 'why' of this elaborate wartime disinformation, but be wary as you watch the slew of poorly researched TV pieces on the London Blitz this month, all of which will probably repeat the myth.