wp-admin of old site kept redirecting to new site

Hello,
I used duplicator to copy website from one folder (A) to another folder (B). Everything i.e. duplicating and recreating, went smooth and website B worked perfectly well.
However when I tried to login to A it kept redirecting to B.
I got a solution elsewhere which fixed the problem:
1) Turned out that homeurl and siteurl for A was set to the B’s url.
2) From phpMyAdmin went to wp_options table and edited and corrected homeurl and siteurl.

Would appreciate if I could know how this happened in the first place? Databases were separate with a different names. Plus why would duplicator go modify the existing website’s table with new websites values. All changes should be on the new website table, right? Did I go wrong somewhere with using the plugin?

Thanks
Roshni