You are not a quintessential INTP or quintessential any other type for that matter, which is pretty clear.
But it seems they base the fact you are an INFP, because your test results are rather random, and that may indicate Fi. Fi strives for integrity and consistency in it's ideals, as a result Fi has a tendency to answer questions on a test conforming those set ideals which can overlap with tendencies of other functions, so that can lead to answering differently.
But I don't really think it's that simple. There are also some things you've said that don't seem INFP to me at all.
It's true your Ti is not pouring out from you, but this is an entirely new subject to you, causing you to have reservations. Makes it very hard for your Ti to come out. So that's perfectly explainable. I'm still behind my latest earlier assumption that you're INTP that uses Te as a shadow function.
I prefer giving you the benefit of the doubt based on your own ability to recognize yourself in the various descriptions. But it's good to keep an open mind and allow for more communication before anyone here, like [MENTION=5143]Salomé[/MENTION] said, can type you effectively. Although, like Salomé insinuates, I don't agree that it is bad for people to share their opinions and observations, wether or not they are right is not the issue, their observations could still share a valuable angle of perception that can lead to useful discoveries. In your case, if they feel you appear Fi, it might just be because you're a bit overwhelmed and aren't really sure what to think, and just need some time to process this all with your Ti and still hold a valuable insight for you. But it might also be because you're Fi. Or that they're plain and simply wrong.
It's up to you to read up and try to understand the various functions and their workings to see which of the two you really are.