The quoted text and the Wikipage page you linked to do not seem to agree on the meaning of the referendum, and the book (and your question) are definitely wrong on "Crimea joining Ukraine" in 1991.
Wikipedia tells us:
The Crimean ASSR was originally created in 1921, as part of the Russian SFSR in the Soviet Union. Crimea was invaded by Nazi Germany during World War II, and when the region was reclaimed by the USSR in 1944, the Crimean Tatars and other ethnic groups were deported to Central Asia, and the ASSR was dissolved in 1945 with Crimea becoming an oblast of the Russian SSR. On 5 February 1954, it was transferred to the Ukrainian SSR. During the collapse of the Soviet Union at the start of the 1990s, the Russian SFSR declared itself sovereign on 12 June 1990 and the Ukrainian SSR declared itself sovereign on 16 July 1990.
In September 1990, the Soviet of People's Deputies of the Crimean Oblast called for the restoration of the Crimean Autonomous Soviet Socialist Republic together with the previous level of autonomy that the peninsula had enjoyed under the ASSR.
So they tell us:
- 1921 - WW II: Crimea was an ASSR within the Russian SFSR
- WW II: invaded by Nazi Germany
- 1945 - 1954: Crimea was an Oblast in the Russian SSR
- 1954 - 1990: Crimea was an Oblast in the Ukrainian SSR
So the question is not whether they wanted to be part of Russia or of the Ukraine or of any other SSR or altogether independent, but rather whether they wanted to remain an Oblast within an SSR, or become an ASSR within an SSR. Since they were already part of the Ukrainian SSR, that means switching from an Oblast in Ukraine to an ASSR within Ukraine. There's no mention of becoming independent from Ukraine, just gaining the "Autonomous" status within Ukraine (of course the ultimate goal could have been independence, but that was not what was explicitly expressed at this point).
And so that's what the Ukrainian (not Crimean) parliament (reluctantly, apparently) did after the referendum: exactly what the people voted for.
The Crimean Parliament later "declared the state sovereignty of Crimea as a constituent part of the Ukraine". But that's not "joining the Ukraine" (they were already part of the Ukraine for decades), that's just going one notch further in their autonomy (normally declaring state sovereignty would be a claim for independence, but they still decided to remain "a constituent part of the Ukraine).
The book makes it appear as a referendum on independence, when it definitely wasn't (it was a move in that direction, sure, whybut it wasn't independence). Autonomy and independence are quite different things (ask Catalonia or Scotland).
I hope the rest of the book is better, but given the synopsis...