Your first amazon link is for a product sold by Amazon.com and the second link (the hard drive itself) is being sold by a different merchant, so they are not comparable as the third party sellers have weird pricing for various reasons.
WD My Book 10TB USB 3.0 External - $185.99 (free shipping) https://www.newegg.com/p/N82E16822234346
WD Red 10TB NAS Hard Disk Drive $283.98 (with $3.99 shipping) https://www.newegg.com/p/N82E16822231546
So it's still ~$100 cheaper. Like I said before, this isn't the only example.
I also found this conversation while trying to find out kind of HDD it is:
https://www.reddit.com/r/DataHoarder/comments/8ghb0o/wd_mybo...