This is true at Humboldt. Arcata is a legitimate California “college town”. It may not be as large or well-known as Berkeley or Palo Alto, or even Davis, Chico, or, San Luis Obispo, but the local atmosphere is clearly affected by a large percentage of student and faculty residents.
In contrast, you may not find a college town atmosphere at CSUMB. As noted above, the campus occupies only a portion of a large former military base. It is surrounded by undeveloped portions of the former base. The nearest communities (Seaside and Marina) are not noted for any collegiate vibe.
Another indicator of UC/CSU social activity: does the campus support a football team? You may or may not personally care for football, but if thousands of students turn up on campus on Saturday for a game, it does suggest that there is a level of interest in school activities that goes beyond just showing up for classes.
Most UC/CSU football teams are in the largest metro areas: Berkeley, San Jose State, Sac State, Fresno State, UCLA, San Diego State. But there are three exceptions: Davis, Cal Poly, and Humboldt State. All three are located in smaller towns outside the big cities – but they are college towns with lots of student life.