Why do t-butyl bromide and silver(I) nitrite form the nitroalkane, not the nitrite ester?

We know that reaction of $\ce{AgNO2}$ with alkyl halides is SN1 type reaction and follows HSAB principle. So in the reaction of $\ce{(CH3)3C Br}$ we would expect $\ce{AgBr}$ to form and also a carbocation $\ce{(CH3)3C+}$. 


According to HSAB, since the electrophile is *hard*, we expect the *hard* nucleophile to attack. So attack is expected from *oxygen*, and expected product is $\ce{(CH3)3C-ONO}$


**But** my book states that reaction product is $\ce{(CH3)3C-NO2}$. Why is this product formed?


