Example:
Account X with BTC100
You send BTC1 to Account Y
Account Z is created by your secure wallet
BTC1 will be sent to Account Y
BTC99 will be sent to Account Z
Your remaning balance is now in account Z
The stats say BTC100 was moved even if BTC1 was actually sent out to a foreign account.
P.S. This is done to protect your public key aswell as your private key. Only when BTC is sent does the source address need to provide it's public key.
Nicely explained!
And the more corn there is in an address, the more skewed the results will be, e.g., imagine one has BTC100000 in an address, and sends only BTC0.01 somewhere... Although only BTC0.01 was actually sent out, a whopping BTC100000 was moved.