Passwords being sent in clear text due to users’ mistake in typing it in the username field

Upon reviewing the Logs generated by different SIEMs (Splunk, HP Logger Trial and the AlienVault platform’s SIEM) I noticed that for some reason quite a few users tend to make the mistake of typing their passwords in the username field, either in the OS Domain logon, or within web applications. I am guessing those are people who cannot type without looking at the keyboard and in trying to do so, doing it fast, end up typing their passwords in the wrong field. This means that the password is sent in plain text everywhere in the network and end up recorded on the logs with an event that says something along the lines:

What is the difference between authenticity and non-repudiation?

I’m new to infosec and doing some reading. Not surprisingly one starting point was wikipedia. In this article, authenticity and non-repudiation are listed as 2 separate ‘Basic concepts’. My understanding is that you cannot achieve non-repudiation by not knowing which parties are involved, which requires authenticity to be in place. In that sense, I see authenticity as a sub component of non-repudiation.