The linked article says "The bot received incentives for winning and basic metrics like health and last hits". So apart from losing/winning, losing health is bad, last hitting is good. You could add more, but apparently that's all OpenAI used.
(1) Not creepblocking at all, and letting your opponent have your creeps under their tower
(2) Modest creepblocking to punish (1)
(3) Severe creepblocking to punish (2)
Would be better than some hand-trained RL creepblocking which is divorced from game outcomes.