How can someone have 1,649,892 points on Yahoo, questions and answers ?

If members have very old accounts, it can be possible to achieve over 1,600,000 points on YA. They would have to answer more than ask, self vote when we could, and likely answer simple 1 word posts.

There are seven users with over a million points in answers.

The one you are referring to has been here since December of 2007, you can get a lot of points in that many years.

Up until a few years ago there used to be unlimited q and a for levels 6 and up and you also got to vote for your own answer. Points added up very quickly in those days.

if they have an old account it's not impossible

simple you can go to any number with cheat engine seen it done.