confluent status does not report the status of Zookeeper started by zookeeper-server-start

[yaojingguo]

I start Zookeeper with bin/zookeeper-server-start -daemon etc/kafka/zookeeper.properties.

$ echo srvr | nc localhost 2181
Zookeeper version: 3.4.13-2d71af4dbe22557fda74f9a9b4309b15a7487f03, built on 06/29/2018 00:39 GMT
Latency min/avg/max: 0/0/0
Received: 1
Sent: 0
Connections: 1
Outstanding: 0
Zxid: 0x0
Mode: standalone
Node count: 4

But confluent status shows:

confluent status
This CLI is intended for development only, not for production
https://docs.confluent.io/current/cli/index.html

ksql-server is [DOWN]
connect is [DOWN]
kafka-rest is [DOWN]
schema-registry is [DOWN]
kafka is [DOWN]
zookeeper is [DOWN]

I am using confluent-community-5.1.0-2.11 with JDK 1.8 on macOS 10.13.6.