Q: What can be the reason behind two papers by the same author having similar content ?

Two papers authored by the same person having the same titles and similar content certainly cannot be a coincidence. There can be several possibilities:

1. It is possible that one of the papers is a conference paper while the other is a full-fledged journal paper on the same topic, which is perfectly ethical.

2. Alternatively, it could be that parts of one paper have been used in the second paper. In that case, if the author has cited the first work, then it is an ethical publication. However, that seems unlikely as the titles would not be the same in that case.

3. The journal where the second paper was published would probably have done a check for plagiarism. However, the possibility of self-plagiarism cannot be completely ruled out.

4. It could also be a case of duplicate publication where the author had submitted the two papers to two different journals around the same time, and both were published.

However, you need to check the details very carefully before you come to a conclusion. If you feel inclined, you could possibly write to the editor of one or both journals and point out the overlap. This would lead the journals to investigate the matter and take necessary action if required.