why is this not spam?

[Trevor Smith]

So I've got bogofilter working, more or less, with KMail and a message with 
this header line ends up in my inbox:

X-Bogosity: No, tests=bogofilter, spamicity=0.987305, version=0.92.2

Why is a message with spamicity=0.987305 considered "No" in terms of bogosity?

I haven't set any spam or ham cutoff values (so they are at their defaults, I 
guess).

Doesn't the above qualify as a "very" likely spam? What am I missing?