Are you sure that's wrong?
If I plug in “timeInMilliseconds” => 1504111665465, value into https://www.epochconverter.com, I see:
Assuming that this timestamp is in milliseconds:
GMT: Wednesday, August 30, 2017 4:47:45.465 PM
And your @timestamp value:
"@timestamp" => “2017-08-30T16:47:45.465Z”
Looks spot on to me.