DS is a freshman at Caltech now. He also played video games occasionally as a social thing in HS. He doesn’t do math problems for fun, he has enough in his homework. He doesn’t have a lot of free time now but partly because of “hurdles” which are problems you need to solve to get into the famous Ph11 class. Most students don’t bother with them, so I guess that may count as programming/doing math stuff in your free time. He does have a group of friends, and their house organizes some fun activities on weekends. He played table tennis, badminton, other sports as recreation. Others may spend their time differently but it’s easy to meet people and find someone who shares your interests. Drinking does happen but is easily avoided. Pranks are popular and encouraged. Generally I think he found out other students at Caltech are all very intelligent but not necessarily off-the-charts geniuses who do nothing but STEM (as he probably imagined).
Caltech very much encourages undergrads to participate in research. Collaboration and honor code are also big deals. Most homework is done with others, and all tests are take-home. One thing I imagine may be better at Mudd is teaching quality. At Caltech you can have a freshman class taught by a Nobel winner, but the general teaching quality is hit or miss as far as I can tell. DS enjoys most of his classes though.