While I agree with you that the list was most likely not intended to be complete, I don't understand your argument that the use of the word "can" proves our case. In regards to whether a list is inclusive or exclusive, I see no difference at all between:
"The following factors can break concentration:"
and
"The following factors break concentration:"
I can see where the inclusion of the word "can" makes a difference in whether the list is permissive/mandatory or possible/certain, but try as I might I just don't see any way it has a bearing on whether the list is inclusive or exclusive.
In my experience, a determination of inclusivity/exclusivity usually relies on specific langauge to establish inclusivity, such as "such as", "for example", "here are some", "etc." etc. Otherwise I find that the general presumption is that lists are exclusive. In this case, however, I agree with you that the designer intent was that the list be inclusive, both because of the broad scope of the final list item (although from a technical standpoint that could also be construed as an exclusive list including a residual clause) and also because of the general design philosophies behind 5e.
I just don't understand how the inclusion of the word "can" is even relevant, let alone dispositive.
Hmm. Okay, so, I can come up with a sort of example.
"Is there any way to view the source of a web page?"
"Firefox can view source."
This doesn't actually remotely imply an exhaustive list, and you might even interpret it, in that context, as implying there's probably other things which can also do that. But I think, in that case, it's not "can" that does this. It's the context of not having any kind of qualifier or introducing a list. In general, if you introduce a list and intend it to be non-exhaustive, there's usually some kind of marker like "some examples are" or "for instance".
But I've seen sentences where "can" may have had a sort of connotation of "well, this is one way to do it".