Nope. If you are not part of the group, then that post option itself will not be available. I have asked support on this issue.
As a work around, try to logout of the App, login and try again. Also try commenting from browser and see if it works.
All-in-one Pack Support
Report
There was a problem reporting this post.
Block Member?
Please confirm you want to block this member.
You will no longer be able to:
See blocked member's posts
Mention this member in posts
Invite this member to groups
Message this member
Add this member as a connection
Please note:
This action will also remove this member from your connections and send a report to the site admin.
Please allow a few minutes for this process to complete.