Thanks Manish bhai. It was post by Vaihav sir in his post on March 30, 2016.
/blog/post/1373404 and not on March 29. Moreover, SBG was not tagged. Therefore, it was not visible on SBG forum. I wished anybody had captured it. I am not in town so it was not possible for me.
Only one green/red flag per member is allowed, as you cannot have two views on the same thing. However, one can always raise a question to the creator of imaginary train about the issues and then provide a flag accordingly.