Hi,
There is no problem at all.
The first product have two images.
The second product have one image per variant.
If you change the variant the thumbnail can also change.. But because all of your variants have images, the images of the main product are not used, they are overriden.
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.