Did you read the report? Policing is still a major part of the Swiss approach to drug prevention (one of the four pillars) and though they try to use fines as a penalty instead of imprisonment, imprisonment for drug use still happens as well:

> It is notable that by many measures, policing did not decline with the advent of the four-pillars policy. As Figure 2 shows, policing continued to be very active well after the drug policy changes occurred, though the bulk of arrests since the early 1990s have been related to cannabis use by young persons (Reuter and Schnoz 2009). Relatively few of these arrests, however, led to incarceration and many resulted in administrative fines not registered on a person’s criminal record (Ibid.; Killias 2009).