Well, you have to see it in a bit of a context. Many votes in Switzerland are concluded on a much tighter scale. Sometimes stuff gets accepted or declined by 50.5% or even less. 55% against the initiative is pretty decent, especially when it looked like it would pass for a long time. Me personally I would have liked to see 95% against this crap, but this has never happened on any matter that was voted on, so...
Also, the cities and suburbs, with the supposed "problems of immigration" right in front of their doorstep, all declined the initiative. It was the country side and small communities that aren't even affected by immigration, that voted for it. This shows once again, that fear is a powerful tool to mobilize masses. Thankfully it didn't work this time but we gotta stay alert and fight the narrative of fearmongering every single day.
Source: Me, I'm Swiss.