As far as I know, sometimes, your account may also get locked if you change password numerous times, it's an automatic process, if the bot identify your activities as suspicious, your account may get locked.
Didn't heard about that automatic process. But when a user changes their password they get an email saying ''if you didn't change your password you can lock your account by clicking this link.''
I think OP clicked that link accidentally or he used an open-source email like yopmail where anyone can visit and click that link.