Indeed this is a huge decision you alone have to make, and you must make this decision on free of doubt. My suggestion is that the both of you all really come together and talking this throw. Understanding and respecting each others point of view's...before it's too late.
If he is needing you to affirm that he is the one, and you are questioning his intent already. I would put off any vowtaking and continue to get to know each other a little bit more. Whats the hurry? You both are making a huge decision in committing to each other for the rest of your lives, yet it sounds like neither one of you are ready emotionally to take that step. Just because you get married does not necessarily mean the marriage will work so save yourself a lot of grief and take a step back. Allow the time it takes to erase the question marks.
I would be wondering in your shoes if I myself (not him) am ready to be engaged, at 19. In the next 4 or 5 years, you are going to change a lot and develop as the adult you are going to be. A good marriage should last 50 or 60 years, are you certain that at 19 you can say this is it?
Communication is not----- I repeat NOT---------- a reason to end a relationship. He asked you a question. Maybe he felt insecure at that moment. Maybe he just wanted to affirm what he thought. And sometimes it just feels nice for someone to say "yeah, I'm so glad I'm with you vs. anyone else." Not a big deal.
Make sure you aren't looking for a reason to end the engagement.
good luck