Webhook build is triggered regardless of Trigger Condition.
In the source code, although the condition is false, only warning is logged and keep going.

/* JiraWebhookResource.java */
private void triggerBuild(Configuration configuration, Map<String, Object> context) {
    ...
    if (!start) { // start is the result of evaluating Trigger Condition.
        log.warn("No need to start build due to build condition not match, configuration: {}", configuration);
        return; // should return because 'Trigger Condition' is false
    }

    BuildRequest request = new BuildRequest();
    ...