The app does not calculate shipping weights.
If you have "Requires shipping" enabled in the Product options settings for your bundle (see screenshot below) then the app will use your default shipping options/charges that are applied in your Shopify theme's admin and in your product settings.
This includes the weight calculations for shipping.
Here's how to find the location shown in the screenshot below:
1. Admin 2. Apps → Bundle Builder 3. Choose your bundle 4. Under “product options” toggle the "requires shipping" checkbox.
Please do not add manual weights to the bundle's Dummy Product Page.
These will be overwritten by the app as the app will only use the default settings in your theme/product listings.