Probably that both keywords have the same meaning / intent and they cannibalize on each other.
For example, keywords like "where to buy [whatever]" / "where can I purchase [whatever]" have the same meaning / intent (buying the [whatever]), despite of using different words. In such cases, if you create 2 different pages on your site, with each page being optimized for its corresponding keyword then one of your pages cannibalizes on the rankability of the other page, which leads to google not knowing which page to rank, so they're probably ranking the page that is either...
a) better optimized for its corresponding page (in your case that'd be page 1 being better optimized for keyword 1 than page 2 being optimized for keyword 2)
b) more relevant to its specific keyword (if both keywords have the same intent this scenario is probably the least possible, but it's a possibility still, which is why I mention it)
c) less competitive (many times, 2 keywords with identical meaning can have different difficulty scores, so it's possible that in your case keyword 2 is harder to rank than keyword 1, all things being equal, so google chooses to rank page 1 for both keywords because they both have the same meaning)
So, if both of your keywords have the same meaning just keep one of the pages (preferably the one that already ranks, which is page 1 in your example), and delete the other page and be glad that you're ranking for both keywords (just make sure that you remove the internal link in this case since it will point to an invalid URL and that's bad)
If the 2 keywords have different meanings / intents, though... well, that's pretty weird and I have no answer to your issue, unfortunately.