Because he's making a red ale and amber ales are a different thing but people are loose with the definitions. In a red ale you want crystal malt. Amber is more for milds so you dial down the hops quite a lot more.

One solution would be to replace some or all of the flaked oats with oat malt which gives you diastase. I've just made V2 of mine. Pale, roasted barley, oat malt, flaked oats, wheat malt for head, Chocolate malt. It is VERY black and oily wort but V1 is pretty good. That had no oat malt, lots of...