Garmin literally says that elevated stress levels can be from good or bad experiences in its description of the feature. The author started from a faulty premise.
> For example, elevated stress levels may stem from pressure at work, social anxiety or from something as simple as encountering an aggressive driver on the highway. Elevated stress levels could also be the result of happier situations, such as the excitement of a new job, the thrill of a first date or the jitters a runner feels the morning of a big race. Keep in mind that excessive exercise, consumption of stimulants, poor nutrition and getting sick can also produce higher than normal stress levels.
https://www.garmin.com/en-US/garmin-technology/health-scienc...
> For example, elevated stress levels may stem from pressure at work, social anxiety or from something as simple as encountering an aggressive driver on the highway. Elevated stress levels could also be the result of happier situations, such as the excitement of a new job, the thrill of a first date or the jitters a runner feels the morning of a big race. Keep in mind that excessive exercise, consumption of stimulants, poor nutrition and getting sick can also produce higher than normal stress levels.