Free samples are nice, but with with gifts that could be taken the wrong way it would have been better to mention the specific gift before ordering. That is, if it is not a targeted gift and given with all orders.
I think it is more likely that this is a targeted gift. Atkins gave the bars to Forever21 for free or at great discount if they where given to people that ordered plus sized clothing. That makes more like fat-shaming.
This does make a fine example of how targeted advertising can hurt real people though.