congrats to a safe landing!

back when i owned a cherokee 140, i planned for such an event
by considering what i would do under similar circumstances. my plan
was to either (1) intermittently shut the fuel off, at the fuel
selector
or (2) intermittently pull the mixture to full cutoff, and cycle as
needed.
if the prop did stop at glide speed, i could just key start the
engine.
you are lucky to still have had power available; i've heard of
circumstances where the throttle "wire" became disconnected from
the carb butterfly arm (due to a loose screw) and the power went to
idle in flight. (at every annual, i would check to confirm this screw
was
tight!) i've never heard of a "spring" that would cause the throttle
arm
to open wide (on a cherokee 140, am not sure about the 140 "cruiser").
i've also heard of the throttle knob and wire coming completely back
from the instrument panel into the cockpit, due to a loose carb screw.

my prior experience with a C172 i once owned, was that the prop would
not stop turning in flight, with the mixture pulled to full cutoff and
the
plane at glide speed (but this was with a 6 cylinder engine). in
fact,
i experimented (to learn my plane) and determined (with plenty of
altitude) that i could not get the prop to stop turning, even during
normal stalls (with the mixture at full cutoff); i had to pull the
bird up
into a hammerhead stall, to get the prop to stop turning (i was over
an uncontrolled airport at the time, for my safety). also, i
determined
that, with the prop stopped, i had to dive to an airspeed over 100 mph
indicated, to get the engine to start windmilling again (once the
airspeed
pushed the engine past that first cylinder's compression, the prop
rotated). (yes, i am aware of engine cooling situations such as
this.)

it appears, from your post, that the prop (on a 4 cylinder engine)
stopped
during flare, so the 4 jug engines apparently react differently to
airspeed
than do 6 cylinder engines.

DISCLAIMER: AM NOT RESPONSIBLE FOR ANY ACTIONS YOU
TAKE TO EXPERIMENT WITH YOUR PLANE. YOU LEARN FROM
YOUR EXPERIMENTS, AT YOUR OWN RISK.