Non-Responsive Consumer Doc Polishing

This was a problem with early versions of the clients; the code
remains in case some other reason causes the poll to hang.
Clarify the docs.

spring-kafka-docs/src/main/asciidoc/kafka.adoc

@@ -2928,8 +2928,8 @@ public ConcurrentKafkaListenerContainerFactory kafkaListenerContainerFactory() {
 
 In each of these cases, an event is published once per minute while the container is idle.
 
-In addition, if the broker is unreachable, the consumer `poll()` method does not exit, so no messages are received and idle events cannot be generated.
-To solve this issue, the container publishes a `NonResponsiveConsumerEvent` if a poll does not return within `3x` the `pollTimeout` property.
+If, for some reason, the consumer `poll()` method does not exit, no messages are received and idle events cannot be generated (this was a problem with early versions of the `kafka-clients` when the broker wasn't reachable).
+In this case, the container publishes a `NonResponsiveConsumerEvent` if a poll does not return within `3x` the `pollTimeout` property.
 By default, this check is performed once every 30 seconds in each container.
 You can modify this behavior by setting the `monitorInterval` (default 30 seconds) and `noPollThreshold` (default 3.0) properties in the `ContainerProperties` when configuring the listener container.
 The `noPollThreshold` should be greater than `1.0` to avoid getting spurious events due to a race condition.

spring-kafka/src/main/java/org/springframework/kafka/event/NonResponsiveConsumerEvent.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2017-2020 the original author or authors.
+ * Copyright 2017-2022 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -25,8 +25,8 @@
 import org.apache.kafka.common.TopicPartition;
 
 /**
- * An event that is emitted when a consumer is not responding to
- * the poll; a possible indication that the broker is down.
+ * An event that is emitted when a consumer is not responding to the poll; with early
+ * versions of the kafka-clients, this was a possible indication that the broker is down.
  *
  * @author Gary Russell
  * @since 1.3.1