The most nearest case would be OP clicking on the lock account link in the password recovery email mistakenly. 
I don't think so, I think a locked account won't be shown on any public logs bpip scraped data from seclog and modlog, autoban was on modlog
so I'm pretty sure he has broken a rule, plagiarism, spam or ban evasion, that made him get banned by mod
I see, from the dates of getting banned and the reset of password, it is clear that he tried to change the password of an already banned account, which was surely for breaking some forum rule.
Quote from: https://bpip.org/profile.aspx?p=lega46141
3/3/2019 8:45:04 AM password reset via email
2/13/2019 8:59:16 PM Changed to Archived status Autoban user
2/13/2019 8:59:16 PM Changed to Archived status Autoban user
And yaa, locked status doesn't seem to be updated in the mod log and not indicated publicly anywhere.