I was pointed out that this was not clear as stated below:
The flow is explicitly stated to be a "profile of The OAuth 2.0 Authorization Framework" (section 5.2.1 of profile 2), which does not have a hybrid flow. The behavior of the AS in the rw-flow is inherited from the AS of the r-flow, which is an OAuth 2.0 profile. As we see it, in the case of a r-flow, the AS only returns an id token if the scope contains openid. Therefore, we assumed that this also holds true for the rw-flow.