I assume by "misleading" you mean misrepresenting. Information is exchanged here regarding potentially life threatening situations. If someone is misrepresenting aspects of who they are, they may be lying in other ways as well. While their identity/credentials are irrelevant to the validity of their statements, their readers are entitled to know the truth and make their own judgments on accurate information. Inaccurate information is worse than incomplete information - posters are free to conceal their personal information, and the reader can take that for what they will, but false information cannot be judged if one doesn't know it's false.
Should you reveal the truth? Do you owe this person some sort of confidence? Are you his attorney, priest, or physician? what makes you think you are obligated to support his lying?