Norwegian doesn't have a separate continuous present form like English does, so most present tense sentences in Norwegian can translate to both the English simple present and the continuous present. Of course one tense will often make more sense than the other, depending on the context.
- "drink" and "drinks" are both simple present, just different verbs to go with different subjects.
- "is/am/are drinking" is the present continuous, and again have to agree with the subject.
In Norwegian, there's only one present tense and no verb agreement, so they all translate to "drikker".
If you're on iOS and haven't updated in a while, you may want to update now. There was a recent issue with the letter "i" not being the same as the standard "i", and thus registering as a mistake.
If that's not the case, it's probably Duo being buggy. If you're really stuck, it often helps to do the lesson on another device; PC if you're on a phone and vice versa.