"Doing keto" implies less than 20g/day on an ongoing basis, at least as I understand it. On top of that, one might have eaten early in the previous day, eaten no breakfast, and be working out about lunch time, which would provide the "at least half a day without carbs of any kind".

It may be that you disagree, but I get the feeling that you ignored the "doing keto" part of my setup, and instead thought that the person in question was eating cake 12.5 hours before the workout. :)