I don’t think Apple has anything to worry about there is just no eco system that works together like Apple products yet. I’ll say this though me personally I like the Fossil Explorist wrist watch, I’ll be taking a closer look at it.
To be fair Fitbit was mainly focusing on fitness trackers/bands and smartwatches...they only tried to compete with the Apple Watch in recent years. But no, Apple shouldn’t be concerned with potential Fossil rivals...at least not for now.