I believe your IO make it too simply in answering no need
to declare.
It actually depends on the question pose.
If ask, have you ever been charge in court of law : the answer
is no
But if the question is have you ever been arrested : the answer
could be YES.
But as it was let off with a police warning only, the answer
could be a Yes and No... depends where and by whom the question is
ask.
By the way, yours police warning is not consider a record
lah