Sorry in advance for my poor English, I am not a native speaker. If I made any part unclear or ambiguous, please comment and I will try to elaborate.

I got a message from System mentioning that my submission 131185521 significantly coincides the submission 131179762, which was submitted by mig, a user whom I don't know.

Yes I have to say that two submissions are quite similar, but it's because the problem is expected to be solved in this simple way (convert $$$k$$$ into base-2, then treat the binary string as a base-n number), and we both, coincidentally, choose to construct the answer starting from the least significant bit of the binary representation of $$$k$$$, in a very common way.

I never search for or try to search for any public accessible solution code during a contest. I code on my local machine and never publicly published my solutions to the Internet, not to mention unintentionally leaking solutions during a contest.

The message I received stated that I should have conclusive evidence that a coincidence has occurred due to the use of a common source published before the competition, but it's not the case, we just both implemented a common bit manipulation procedure, on a simple problem, by pure coincidence.

That's all I want to say, this is my first time faced with such kind of problem, so I am not quite sure what else should I do, or who should I contact now.

Any help is appreciated, thanks.