I'm sure personality types play a factor, but I'm not even sure if that alone can account for the differences in interpersonal attitudes within the programs. I think that program/institution culture plays a huge role in shaping these relationships and is also something that is often passed down from upperclassmen to underclassmen -- even shaped by the teachers themselves.
In my nursing school
program, there were "class representatives" that were designated for each cohort and we noticed that they essentially shaped the culture of each class. For example, in our class, we would basically pool our notes together, have student-led study sessions that were open to all, and huge student-organized celebrations at the end of each semester. There was a lot of unity and friendliness that was noticed by even the faculty.
The class that came in after us however was extremely cutthroat! Nobody even ended up running for their representative until student council prodded them to do so. I kept in touch with friends who got held back and had to be placed into the newly entering cohort and they described a very survivalistic mentality where everyone was competing for the same jobs. It truly surprised me what a change it was.
I suppose these are sort of two extremes, but an interesting dynamic I noticed nonetheless!