Yes they are referring to that, but the method for creating a stock solution is the same. And all you are doing is overdosing the fish in anaesthetic .
You still need to create the 1:10 mix (1ml clove oil to 9 ml ethanol) to then dilute down again into water, it is the volume of stock (1:10) solution diluted in water which creates the final does for euthanasia or anaesthesia. Clove oil is still Hydrophobic and to be effectively dissolved in water needs to be dissolved in a solvent first.
This is one of the main reasons why it is not approved for use in the UK science world, nor is Benzocane which is also hydrophobic. They don't readily dissolve in water, their anaesthetic effects are highly variable and between and within species and because of the dilution, efficacy can vary within a created batch.
Regardless of whether you are talking euthanasia or anaesthesia, the method for creating the final solution is the same. As I am sure we can all agree this is a serious topic where we don't want the animals to suffer, thus doing this properly and understanding why is essential.
Don't get me wrong, you can euthanize by just adding clove oil into water, but you run the risk of oil adhering to the gills and suffocating without any anaesthetic effects, it not being totally effective, or taking too long and stressing the fish.
For euthanasia fish need to be in an immobile state within 10-30 seconds to reduce suffering and stress. to do this you need to be as effective as possible, thus using the correct method is important.