Hi,
The related products module is actually not displayed by your template. It's displayed directly by HikaShop. That's why it is displayed on the product page even if it is disabled in the Joomla modules manager.
And since it's displayed directly by HikaShop, we properly check as to not display the title of the module if there is no content to display.
So I don't think that looking at the code of the HikaShop will help in anyway since there is no chrome system for that in HikaShop.
It really has to be checked with the template provider or by a 3rd party developer who knows how to customize the PHP of Joomla templates.
I wouldn't be able to tell you what to do exactly since each template does it differently. It would require some analysis of how the template works and how the website is configured. That's why I could only give you a link to the chrome documentation of Joomla, which is the closest thing useful in this instance.