Of course Yoshi is going to give vague answers to several lore related questions.

1) he is unsure whether some plot points/threads will be revisited in the future content
2) the ancients being as popular as they are, certainly makes it appealing to the writers to hamfist them in somehow in the future
3) he doesn't want to step on too many toes with giving straight-forward answers since fan content, theories and analysis are a good way to keep the game afloat and people talking and actively interacting, thus him only giving his interpretation on lore related questions, without necessarily squashing (popular) fan theories in the process.. of course, there are people who feel they've been personally wronged by the story already, so it might also just be light backtracking