You have correctly identified the problem. The FamilySearch Wiki article is in error and has directed you to the wrong periodical.
Ancestry's About the Database information says:
About South Carolina Magazine of Ancestral Research, Vol. 1-20 Founded in 1973, the South Carolina Magazine of Ancestral Research is
designed to aid the researcher of southern ancestors. Articles contain
information on a wide range of topics from royal grants, to tax
records, to obituary notices in local newspapers. This database
contains the first twenty volumes of the serial. Specific inquiries
regarding particular articles and further information can be directed
to Brent H. Holcomb, ed., P.O. Box 21766, Columbia, S.C., 29221.
However, if you follow the links from the Wiki to The South Carolina historical and genealogical magazine at the Internet Archive, the publication information at archive.org says:
The South Carolina historical and genealogical magazine by South
Carolina Historical Society
Publication date 1904 Topics genealogy Publisher Charleston, S.C.
[etc.] South Carolina Historical Society
Note the publication date. It might be possible that someone in 1977 reprinted a copy of a publication from 1904, but as you already noted, the titles do not match.
To find SCMAR, you have several options:
Let's recap. The Ancestry Record page you cited says:
Name: John Knight
Marriage Date: 1675-1858
Source: South Carolina Magazine of Ancestral Research, Vol 5, # 3
From the links above, in Dec 1977, contributor Paul R. Sarrett, Jr. submitted this transcription to USGenWeb:
Marriage Records 1675-1858 (large file 326 kb) Some 4,094 Marriages.
Extracted from: South Carolina Mag. of Ancestral Research, Vol 5, # 3
The file is a classic old-school text file abstracting the marriages listed in that volume of SCMAR. Note the file size, it will take a while to load completely.
The transcript has a Soundex code followed by the name for both groom and bride (where the bride's surname is known), followed by a marriage date. Here are all the Knight marriages:
K523 KNIGHT, JHN G225 GASCOIGN, SARAH Oct 31 1771
K523 KNIGHT, JOHN , MARY
K523 KNIGHT, JOHN A536 ANDERSON, RACHEL Jan 06 1774
K523 KNIGHT, SAMUEL G520 GINNIS, ANN MRS Feb 08 1778
K523 KNIGHT, WILLIAM G653 GRANDON, ELIZABETH Oct 15 1768
Unfortunately there is no marriage date for the entry you want. My guess is that your John Knight who married Mary are not a couple whose own marriage date is given in the article, but they are listed because they are the parents of a bride or groom and their names appear in their child's marriage record. If that is the case, it may explain why Ancestry gave a date range spanning the entire article instead of a specific marriage date. You would have to find a copy of the magazine and see the original to see if my hypothesis is correct.
Not surprisingly, this abstract of abstracts doesn't give you any context so you can tell where in South Carolina this couple may have lived. To see the record in context, you'll have to find the issue of the magazine, or get hints from the Table of Contents from online sources like this listing at AncestorStuff: South Carolina Magazine of Ancestral Research Vol. 5
Apparently the Allen County Public Library's Genealogy Center does not have SCMAR; it is not listed as an available periodical in PERSI at Findmypast, so I could not use PERSI to find a list of article titles for SCMAR Vol 5.
Your instinct to seek out the original magazine is correct. We should always try to use indexes to find the record hidden underneath. Keep good notes of where you are in the process of tracking down the originail, and remember to cite what you actually saw.
Further reading (all articles by Elizabeth Shown Mills, from her Evidence Explained website):