Moreover, at the same time I got remarked by a person for making duplicate issues and off-topic discussion.
Stack Exchange sites that are not meta sites (e.g. this very site is the meta site for Drupal Answers) are not for discussions.
On Stack Exchange sites you ask, "practical, answerable questions based on actual problems that you face." The FAQ says also, "chatty, open-ended questions diminish the usefulness of our site and push other questions off the front page." You don't ask for other users' opinion, but you ask them to use their expertise to resolve an actual problem you have.
What you are describing in the question is clearly a bug in the module; a module is not supposed to throw a warning about a wrong argument passed to
foreach(). Questions about bugs on modules are considered off-topic on Drupal Answers; the reason is that Drupal Answers is not a replacement for the issue queue for the module, which is the only place the project's maintainers check for issue reports.
If it were not considered off-topic, the question would be too localized, as when the bug is fixed, the question is not anymore relevant to the future users. Questions on a Stack Exchange are not only for the OP, but also for future readers; that is the reason one of the closing reasons is, "too localized."
You are then asking which line is exactly causing the error, and that is another reason to consider the question too localized. How much users would be interested to know which line causes the error? Most of the users are interested in seeing the bug fixed.
The line number is already reported in the error message ("line 1641 of /sites/all/modules/field_group/field_group.module"); if you look at the source code of the module, which you installed, you would know what function is causing that error.
The question has been closed by a single user, but I would have closed it too for the reasons I reported here.
About the down-vote, that is automatically casted from the Community user for questions that are closed as off-topic. In your specific case, I don't see any down-votes, though.