A client of ours is looking to implement a system similar to this custom bundle builder, exactly like that of the linked online store above. This definitely looks like a Shopify store, is anyone familiar with the addon used to allow this?
From what I can see it seems that the store you referenced is using 'Advanced Product Options' by Mageworx: https://apps.shopify.com/advanced-product-options. Although the page you linked appears to look like a bundle of multiple products, this is technically a single product that has custom options.
Hopefully this helps!