OverloadException in single node cassandra - cassandra

Question

I read through this page : https://docs.datastax.com/en/cassandra/3.0/cassandra/operations/opsRepairNodesHintedHandoff.html and identified that OverloadedException in Cassandra is due to the
"The coordinator tracks how many hints it is currently writing, and if the number increases too much, the coordinator refuses writes and throws the OverloadedException exception."
But I use a single node and able to get Overload exception frequently so what could be the reason for Overload exception in singlenode with Consistency as 1 and ReplicationFactor as 1?
EDITED :
Total hints In progress JMX
I checked in the code :
private static void checkHintOverload(InetAddressAndPort destination)
{
// avoid OOMing due to excess hints. we need to do this check even for "live" nodes, since we can
// still generate hints for those if it's overloaded or simply dead but not yet known-to-be-dead.
// The idea is that if we have over maxHintsInProgress hints in flight, this is probably due to
// a small number of nodes causing problems, so we should avoid shutting down writes completely to
// healthy nodes. Any node with no hintsInProgress is considered healthy.
if (StorageMetrics.totalHintsInProgress.getCount() > maxHintsInProgress
&& (getHintsInProgressFor(destination).get() > 0 && shouldHint(destination)))
{
throw new OverloadedException("Too many in flight hints: " + StorageMetrics.totalHintsInProgress.getCount() +
" destination: " + destination +
" destination hints: " + getHintsInProgressFor(destination).get());
}
}
1) Is this the only way to get the Overloaded exception ?
2) Why am I getting the Overload exception in single node ?
3) When this checkHintOverload method is called in Single node?
NOTE :
1) My Keyspace has been configured with NetworkTopologyStrategy, Will that be a reason? : CREATE KEYSPACE test WITH replication = {'class': 'NetworkTopologyStrategy', 'datacenter_1': '1'} AND durable_writes = true;
2) hinted_handoff = enabled in cassandra.yaml, Still I wonder will it trigger the hints in Single node, If so why?
3) consistency level is Quorum in this single node
Could any of the three parameter might be a reason for this?