It was our understanding from the original report that the vulnerability was mitigated by AppArmor disabling ptrace, by no user process running as pid 1 inside the container, and because in CF buildpack apps, user processes run as unprivileged users. This is the stance communicated in the CVE report.
However, with some further consideration and updated information yesterday, we decided it would be prudent to patch and release immediately to be on the safe side. This was communicated to the Cloud Foundry Security team.
I'd have to think about this further, but I'm not convinced that would be sufficient protection (accessing /proc/$pid/fd has a different set of access requirements to ptrace -- it's a dumpability check basically). However, since you've already sent patches around it's all good.
Disclosure: I discovered, wrote patches for and helped with coordination of this vuln.