Http request event - How is the a workflow singleton triggered?

[weirdyang]

            // If a singleton, try to acquire a lock per workflow type.
            (var locker, var locked) = await _distributedLock.TryAcquireWorkflowTypeLockAsync(workflowType);
            if (locked)
            {
                await using var acquiredLock = locker;

                // Check if this is not a workflow singleton or there's not already an halted instance on any activity.
                if (!workflowType.IsSingleton || !await _workflowStore.HasHaltedInstanceAsync(workflowType.WorkflowTypeId))
                {
                    if (_logger.IsEnabled(LogLevel.Debug))
                    {
                        _logger.LogDebug("Invoking new workflow of type '{WorkflowTypeId}' with start activity '{ActivityId}'", workflowType.WorkflowTypeId, startActivity.ActivityId);
                    }

                    await _workflowManager.StartWorkflowAsync(workflowType, startActivity);
                }
            }

Am I understanding this code correctly?
First the lock is acquired, and there's another check if the worklow is a singleton. So this is triggered when:

1. the workflow isn't a singleton
2. the workflow is a singleton and there's no halted instances