There's no ambiguity here, it's just awkwardly worded
Let's put together what we know from the two sources, and see if we can make sense of it.
The Equipment list tells us:
A day's ration weighs 2 pounds
Page 185 tells us:
A character needs 1 pound per day (eg this is the minimum a person can survive on)
A character can make food last longer by subsisting on half rations
Put these two together and it is clear that half rations is 1 lb. So let's look at our last piece of information.
Eating half a pound a day counts as half a day without food
This corroborates what we've learned above: if 1 day's minimum (half ration) amount is 1 lb, and you only eat 1/2 lb, you are eating half of the minimum requirement (ie 1/4 of a ration), this obviously can't work, so the game assumes that you only ate for half the day (basically as if you ate all your ration in the morning and had nothing to eat for the afternoon). This is how the game treats "not having enough food*
2 pounds = 1 day's ration, the "right" amount of food for a person to be well fed and healthy etc. Particularly if active
1 pound = 1 day's half rations, on which a person can survive. Eating any less than this means you are hungry (with any associated penalties). 1 pound is the minimum a person can eat without immediate penalty, but may incur penalties if sustained - for example a person eating half rations may be fine for 3 days, then slowly deteriorate due to not getting enough food. Alternately they may not be able to undertake heavy tasks, or may be able to perform fewer tasks per day.
1/2 pound = half a day's worth of half rations, or a quarter of a full ration. Enough to sustain you for half a day, meaning you are hungry for the other half. This carries immediate penalties.
Think of it as 1 pound is 100% of what we need to live, while 2 pounds is enough to be well fed. By extension, 1/2 pound is 50% of what we need to live. Anyone eating 1/2 a pound in a day is eating half as much as they need in that day, so therefore is treated as not eating for half a day.
The above is how I'd handle the perceived inconsistency in the rules: which is to say, I don't believe there is one.
The correct way to handle it in gameplay, in my eyes, is along the lines of the following (as an example of house rules):
2lbs = full rations = no penalty, all actions are normal
1lb = half rations = you're not eating properly, so there are either lighter penalties, penalties that accrue over time, or there are restrictions on your actions. Some combination of
there's a penalty for certain actions (eg a 10% damage/productivity reduction)
there's a limit to how many days you can be on 1/2 rations
both: it's fine for 3 days, but penalties start to accrue after 4 days
there are limits to actions you can take - eg you can rest indefinitely, or it's okay as long as you aren't in battle but you're unable to attack.
You can perform fewer actions per day (ie less energy) but the ones you do perform are normal
1/2 lb = you're not eating enough to even survive = you get severe penalties, eg 10% health loss on the first day, with an additional 5% for each subsequent day (ie 10, 15, 20, 25, 30, dead)
Of course, your own rules may vary, but that's how I'd handle it