I think you're right that the author confused the names.
Zawahiri, I had heard WAS there in '95.
Yes, you're correct, according to Jayna Davis:
"Clarke writes that Al-Qaeda operatives attended conventions in Oklahoma City in the early 1990’s. According to Davis ’ startling new research, Bin Laden’s No. 2 man, the notorious Dr. Ayman Al-Zawahiri, personally visited Islamic demolitions experts residing in OKC in the spring of 1995 to insure the smooth execution of the pending terrorist strike against the Murrah federal complex."
http://64.233.167.104/search?q=cache:y6DfUptD1JUJ:www.jaynadavis.com/press2.html+zawahiri+oklahoma&hl=en