Hello,
When you add an image for a product in HikaShop, you can decide if you want HikaShop to download the URL you gave or if you want to use directly the URL of the image.
In that specific case, HikaShop will use an external image and you won't have thumbnails for them.
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.