I made the same mistake because I thought "bare" and "kun" were synonymous, but according to the exercise hint they are not in this case. However I do know that "I only eat pasta" is "Jeg spiser kun pasta". So I'm partly guessing here but now it sounds like the meaning in this example is something along the lines of "I'll just eat pasta then". Though, I have no idea why that would be so.
Here's hoping for the shedding of more light on this.
It seems to me that "bare" minimizes the importance of something, along the lines of "merely". If a shop assistant asks if they can help you with anything, a possible reply is "Jeg kigger bare" (I'm just looking). "Kun", on the other hand, is more about limiting the number or amount of something, as in "Jeg har kun 10 kroner."
This is just ("bare") what I've been able to gather as a learner. Others may want to elaborate on this, or correct me if necessary.
The issue is not bare vs kun but only vs just in English. The two sentences are the same in English. If the person eats nothing but pasta, in English you can express this with "just" or "only." There may be subtle distinctions between the two Danish words, but "only" and "just" in this instance would be treated as synonymous expressions to mean that the person restricts their diet to pasta.
It's one of several accepted translations, as far as I can see. The problem is the simple present tense of "spiser". Keeping the tense the same, translated to an English simple present tense makes the sentence rather absolute. "I just eat pasta." - "Since the very first bit of food my mother gave to me, nothing but pasta has ever passed my lips and nothing but pasta ever will. I just eat pasta." But that isn't a very likely situation: It's more likely that it's intended as a present continuous. "I'm just eating pasta." - "I wanted to eat potatoes and pasta today, but I didn't have any potatoes and the supermarket was already closed. I'm just eating pasta." However, present tenses are often used to represent the certain future as well So, when trying to avoid the absoluteness of "I just eat pasta.", one might end up speaking about the certain future. "I always eat pasta on my day off, and this is my day off, so what will I eat? I will eat pasta."
I think you're over-egging what you call the "absoluteness" of the simple present there, P. The simple present doesn't have to equate to "always without exception" ("Since the very first bit of food my mother gave me" etc.) ; it also refers to custom and habit -- the application of which may be at very widely spaced intervals. "Sometimes I have very complicated dishes; other times I just eat pasta."
With the issue of "just" vs "only" and given the other discussions here, I find a major issue with this program is the lack of context. It's hard to imagine all the possible translations of any one sentence, but if you create a context, the experience is more meaningful and certain options work better than others for translation.
I agree that context would be helpful if "only" is not going to be alowed as a possible translation.
In English, "I just eat pasta" is equivalent to "I only eat pasta" if you mean that pasta is all you ever eat.
If you mean that pasta is all you are eating at the current time, "I am just eating pasta" is also equivalent to "I am only eating pasta".
However, if what you mean is "All I am doing is eating pasta", then "I am just eating pasta" is not equivalent to "I am only eating pasta". You do have to use the continuous tense in English to convey that meaning, however.