website keep the previous session even after closing browser tab

i'm testing an old website and i'm facing an issue and not sure how to describe well , but here's the scenario :

1- I open the URL for first time

2- I click on any button ( for example Forget my password button ) and page will redirected to Forget my password page

3- I close the browser tab

4- I open the same URL from step 1 ( Homepage URL ) , here it will redirected me to Forget my password page

Why it keeps the session ? i'm not sure what this issue is calling and i can't find similar issue like this one. please don't suggest to clear cache because i have to do this every time + i can't press Back and Next button in the browser.