It’s not that I am upset, or angry. I am just curious to know that where my answer went wrong. I answered someone’s question, he asked for further clarification, I clarified his doubt in the comments section, and he marked my answer as the accepted one. A few hours laters, my answer had a downvote and was no longer the accepted one (no problem with that though).
As you know when people downvote they are not obliged to offer a comment to explain why. This topic has been extensively discuss over on Meta Encouraging people to explain downvotes and there is no chance that will change. This means that we can only guess as to why someone downvoted your answer. I cannot personally see any thing that stands out as demanding a downvote. I guess we will never know.
It might have been better if the OP had waited a while before accepting an answer in case something better came along. It is rather awkward if they change their mind and have to unaccept but it happens. There is no guarantee that the accepted answer is any better than any of the others, I have certainly seen cases where it was not. In this case though I think that on the balance of probabilities the current accepted answer is the correct one given the context of a club in the first decades of the last century.