You are correct, a PR card and PRTD are not travel documents, they are just evidence of status.
See Section 31(3) IRPA which specifically refers to the PR Travel Document as a "travel document" (to be issued to PRs without a "status document" if specified conditions are met).
see
http://laws-lois.justice.gc.ca/eng/acts/I-2.5/page-8.html#h-20
The PR TD is also referred to specifically as a "travel document" in IRPA Regulation 259 (a) (referring in turn to Section 31(3) in the Act).
Notwithstanding this, my sense is not referencing a previously issued PR TD in response to item 14 should be NO problem. (See further observations about "travel documents" below.)
By law, the PR Card and PR Travel Documents are considered travel documents.
In contrast, the PR card is not referred to as a "travel document," even though it is listed as one of the "prescribed documents" which can be used by a PR, in conjunction with a valid passport or other travel document, to obtain permission to board a flight destined for Canada.
IRPA refers to the PR card as a "status document." IRCC also refers to the PR card variously, including "Permanent residence document" and "immigration document." While it is a "prescribed document" for purposes of boarding a flight to Canada, that does not make it a travel document, particularly since it only suffices as a prescribed document for this purpose when presented with a valid travel document.
Otherwise:
"Travel document" is a term itself used variably. Sometimes as a specific term in reference to certain documents with specified legal characteristics, in both statutes and regulations, as well as in formal government information. Oft times it is employed pursuant to a more general usage.
For purposes of the discussion here, the crux of the issue is what sort of documents does IRCC consider a "travel document" in the context of how this term is employed in the form and instructions for making a citizenship application.
Most visas (perhaps excluding temporary visitor visas) must be disclosed in Item 13, or at least the "status" conferred by the visa; certainly this is so for any visas giving an individual status for permanent residence, or to study or work in a country, all of which must be disclosed.
My sense is that item 14 is not asking for visas of this sort, unless they are stand alone documents which one could use in traveling from one country to another. And as long as all visas (other than visitor visas) are disclosed in response to item 13, it should especially be OK to not include those in response to item 14.