The point is that quantities of alcohol that hurt/kill birds aren't illegal, because those quantities aren't dangerous enough to humans to warrant legal action. It's similar to how we don't accept animal trials as all the evidence required to approve a new drug.
Some things kill animals and not humans. Some quantities of substances kill animals and not humans. Knowing that a product kills your bird is cause for investigation or concern, but not a reason for a blanket ban.
Some things kill animals and not humans. Some quantities of substances kill animals and not humans. Knowing that a product kills your bird is cause for investigation or concern, but not a reason for a blanket ban.