This article claimed the referendum was
30041 in favor of switching to approval and 17264 against it
(64-36% among valid ballots).
This is an excellent result and would seem to bode well for
future success for approval voting.
The 64% in favor is a "landslide" in the sense that no US president
has ever won with that much.
In contrast, the UK's May 2011 referendum to switch to instant runoff voting
(called the "alternative vote" in Britain) failed
6152607 (32.1%) to 13013123 (67.9%)
which was an even greater landslide against IRV.
And even in notable USA cases where IRV adoptions succeeded,
it usually won by below 64%. Victories for IRV with 64% or more
have been rare. The three most (?) famous examples were:
San Francisco CA 2002: 55% (enacted)
Burlington VT 2005: 64% (enacted), 2010: 48% (repealed)
Maine 2016a: 52%, 2016b: 54% (enacted)