Travelled with someone and they were so different when I met them again

I seem to find most people talk about friendship breakups because of how their friends are during their travels but has the opposite ever happened to anyone else? I became friends with someone while both of us were backpacking and spent a week together. We really hit it off and I visited them afterwards but they were so different. They were negative and acting like a contrarion constantly. Some stuff I can put for being tired from working again but I was so suprised by some aspects of their personality that were not visible at all when I travelled with them.