Earlier quoted context omitted.
Guaiacol is present in wood smoke. It's maybe being leached out of the charred barrels into the whiskey during the aging process.
Right - it's the barrels that infuse a lot of the flavor.
> Many whiskies, especially those that are made on the Scottish island of Isley, have a typical smoky taste that develops when malted barley is smoked on peat fire. Chemically, the smoky flavour is attributed to phenols, and in particular guaiacol, which is much more common in Scottish whiskies than in American or Irish ones.