Folks, all of this is from numbers pulled out of some IDC analyst's rear end. Their estimates are no better than SWAG's. I should know, I've had to use their reports in a past life. Sometimes they're accurate, as companies will report otherwise confidential numbers so long as they can't be backed out of the reports. However, Apple doesn't play those games and in this case it's explicitly some analyst's best guess. Most analysts badly misunderstand Apple, and when you misunderstand the biggest player in the market your analysis is almost certain to be wrong.
Also, Garmin's growth was from a very low base. It's easy to grow by 300+% if you start from almost zero.