Hi,
Links to product pages can indeed be different as they depend on the menu used to access them, the category from which they are accessed, etc.
That allows HikaShop to properly handle the breadcrumb system of Joomla. It also allows you to display the same product page in different templates, languages, etc.
It's not really a problem to have different links going to the same page. The only issue is with search engines which can treat that as duplicate content and penalize your pages because of that.
That's why , in your products, you can specify a canonical URL which will be the main URL used by the search engine and the search engine will know that all the links where that canonical URL is are in fact the same page, potentially presented differently, and won't penalize it for that.
So I highly encourage you to properly fill that field of your products.