Indeed, almost all trackers come with notifications and in the study notifications are included in the wearable-based intervention.

The result of 50% larger effects in multifaceted interventions versus wearable-based interventions is from a study by Brickwood (2019). In this study, they distinguish wearable-based interventions (interventions that included tools such as regular emails, text messages, online algorithms, or smartphone apps) and multifaceted interventions (using in addition established behavioral change techniques such as group or individual counseling or information sessions, financial incentives, or telephone counseling). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6484266/