Ok, sorry for digging, but let's make this clear:
As soon as you're on the road and not on the sidewalk any more, you expose other people on the road to danger if you're drunk.
I come from the so called greenest city in Europe and many people go by
bike. Each and every weekend, accidents happen because of drunk people
on bikes (or longboards) doing stupid things like cutting lanes,
ignoring lights, driving on the wrong side of the road or weaving into
oncoming traffic.
Bicycles themselves can't cause much damage, but they can make car
drivers reacting in panic so that they steer into a
tree/pole/wall/car... Because of this (far fetched allegory, I know), it
is also forbidden to walk on the highway, you see?
Now, I understand that this was your neighborhood and there was probably
not much traffic going on at night. Still, the warning or reminder from
the cop might have been his form of educating you about the risks of
using things like longboards on public roads when you're drunk.