Why aren't these important stuff talked about before going overseas

Ingki and Corona (sorry for wrong spelling) talking about engagement and marriage and their expectations towards this matter doesn't seem to align. I have a lot of questions! Why didn't they talk about this before the trip? Or did Corona just made an assumption that he's going to propose to her on this trip? Is she just going by assumptions?! Or maybe it's just a storyline to make her look dumb?! Is she just going by assumptions in her relationship to Ingki? Is everything only made up by Corona's assumptions and all that?!