Pixelmator Photo (and all of Pixelmator's other photo editing apps) is powered by machine learning. Machine learning is an oft-used computer business buzzword tossed around by a lot of software companies. In short, machine learning trains computers using information gathered from one collection of data to make determinations, predictions, and decisions about some other data. Pixelmator Photos machine learning has been trained on "20 million professional photos" to make determinations on how best to enhance your photos so they'll look perfect.
This is a companion discussion topic for the original entry at https://www.imore.com/using-pixelmator-photos-machine-learning-enhancements