(I'm not sure about this)
I think receiver using coinbase wallet (may be i'm not sure). Because each and every coinbase wallet having lot of internal transactions with another bit addy.
Eg.: See/calculate all income and outgoin on this address ->
https://blockchain.info/address/15zLFJqBvfZ2F2hxKp1Ljx16vktUvoZpT1 (which is my coinbase wallet) <- you'll get confused. Beacause, you'll see more spent bits then received. But actually what happening is after reached some amount in an address, coinbase community will take it to its circulating hot wallet (they said when i asked in one of my transaction that happened like this). Because in coinbase, you've no rights to rule over you wallet private instead, they'll control your private key. You can watch the internal transactions at blockchain only, there'll be no change in your coinbase wallet unless you spent it). Even you can see a lot of transaction on the above mentioned addy will've some extra address.
(bad english?
)
~Rude Boy