No CA and client certificates, but TLS works

[Joci78]

Dear community,

I don't know the encryption process in depth, but why does the setting given in the subject work?

MQTT Explorer v0.4.0-beta1
Mosquitto v2.0.17

My mosquitto.conf:

listener 8883
protocol mqtt
certfile /etc/mosquitto/certs/server.crt
keyfile /etc/mosquitto/certs/server.key
require_certificate false
tls_version tlsv1.2
cafile /etc/mosquitto/ca_certificates/ca.crt
persistence true
persistence_location /var/lib/mosquitto
log_dest file /var/log/mosquitto/mosquitto.log
log_type error
log_type warning
log_type notice
log_type information
connection_message true
log_timestamp true
log_timestamp_format %Y-%m-%dT%H:%M:%S
allow_anonymous false
password_file /etc/mosquitto/passwd
include_dir /etc/mosquitto/conf.d