Question: aggregateWindow function doesn't work as my expectation

[b7wch]

Data Set:

_start	_stop	_time	_value	_field	_measurementservice
2022-08-04 13:34:00	2022-08-04 13:37:00	2022-08-04 13:34:00	66.06	CpuUsage	Mongo
2022-08-04 13:34:00	2022-08-04 13:37:00	2022-08-04 13:35:00	68.38	CpuUsage	Mongoprod
2022-08-04 13:34:00	2022-08-04 13:37:00	2022-08-04 13:36:00	90.55	CpuUsage	Mongoprod

Query:

from(bucket: "default")
    |> range(start: 2022-08-04T05:34:00.000Z, stop: 2022-08-04T05:37:00.000Z)
    |> filter(fn: (r) => r["_measurement"] == "Mongo")
    |> filter(fn: (r) => r["_field"] == "CpuUsage" and r["service"] == "prod")
    |> aggregateWindow(every: 3m, fn: mean, createEmpty: false)

Query Result:

_start	_stop	_time	_value	_field	_measurement	service
2022-08-04 13:34:00	2022-08-04 13:37:00	2022-08-04 13:36:00	67.22	CpuUsage	Mongo	prod
2022-08-04 13:34:00	2022-08-04 13:37:00	2022-08-04 13:37:00	90.55	CpuUsage	Mongo	prod

My Question:

1. With the query string above, I expected one line data, but actual result is two lines.
2. And I want to know the detail about how the func aggregateWindow works, I can't get more infomation from influxdb's doc.
3. how the parameter every of aggregateWindow split data to windows