Hi,
I'm not sure what you mean.
The image on both of your links is 450px.
Note though that on the second one, you have a white fat border on the image itself (not CSS, directly the image):
monosnap.com/file/i9rGXiYWptADHtOyMcVUQ95CQs9Fhs
Maybe that's why you think the image is smaller ?
If I look at the original image, I don't see the white border, so I suppose that it was in the thumbnail, then the original image was deleted, and uploaded again, but the thumbnails were not deleted and thus HikaShop still uses the old thumbnails based on the old image.
To avoid that and force HikaShop to regenerate the thumbnails you can delete the images/com_hikashop/upload/thumbnails folder via FTP