The summary was talking about the late 1990's, not the late 1980's.
Novell had been almost entirely supplanted by Windows NT server and other alternatives by the turn of the century, largely owing to the fact that just as the Internet was just starting to become the next really big thing, they were still entirely dependent on IPX/SPX instead of TCP/IP.. By the time they corrected this oversight, they had lost such a large percentage of the market in which they were once dominant that they never recovered. They were about relevant in the late 1990' s as Windows 3.1.
You're off by by a few years. NCP over TCP was the default protocol in the late 90's (Netware 5, 5.1). NT 4 started Novell's slide to irrelevance, but it wasn't until Win2K came out with AD that the coffin was nailed shut.