What type of "technique" is it used to detetc anomalies?

Hi

I have just started using the X-pack.
I testing the "anomaly detection" tool. I would like to know what algorithm has been used to detect anomalies. For example,
If it is unsupervised; is it k-means, DBSCAN, etc ?
If it is statistics; is it the mean, the median, etc ?

Thank you

Some relevant videos that will help explain:

30 Min Meetup w/ Steve Dodson:

2017 ElasticON:

https://www.elastic.co/elasticon/conf/2017/sf/machine-learning-and-statistical-methods-for-time-series-analysis

2018 ElasticON:

https://www.elastic.co/elasticon/conf/2018/sf/the-math-behind-elastic-machine-learning