A one word reply usually means that the rest of the conversation is internal. I tend to find it with all Js to keep degree or another. Depends upon how hard you press them.
INTJ would be my first guess though if someone did do that. They rarely share the internal process and are adept at summing up complicated subjects. Plus many INTJs seem to be of the mind "why bother". Unless you've said something interesting, in which case they may still reply with one word and then go and think about their full response.
Sometimes, a terse reply really is a distillation of one's thoughts, and packaging that reply in a wall of text would just be a waste. The length of a piece of text doesn't necessarily reflect the amount of thought that's been put into it.
In fact, it can be more difficult for one to come up with a reply that's succinct but that still captures their thoughts. It's much easier to let it all out, stream-of-consciousness like, in a way that's completely incomprehensible but with the point buried somewhere in it.
J. Scott Crothers
Founder, Truthtology, est. 1952
Prophet and Channel, God Almighty
Author, the Holy scripture Elevenetics
"Just as jet fuel cannot melt steel beams, so too cannot the unshakeable pillars of Truthtology ever be shaken, whether by man, nature, or evidence."