Multiple arguments should be 'or' not 'and' ?

Problem/Motivation

I have a content type with an entity reference field containing a list of products. I want to display these using Views (to be consistent with the site's product search interface)

Using this module, I can't see any products in the View. If I untick "Allow multiple values" in the contextual filter, I do see only the first product.

Steps to reproduce

Created view of Products (search API) with Block display
Add contextual filter on product ID field.
Configure field formatter on products field of promotion content type.

Proposed resolution

Per the help from the Multiple Values option:

If selected, users can enter multiple values in the form of 1+2+3 (for OR) or 1,2,3 (for AND).

The code for handling multiple values in the field formatter joins the arguments with comma, i.e. AND. This seems like it should clearly be + instead, because none of the products have all of the IDs. When I change to +, the view renders all the expected products.