Not quite. Let’s say I have two profiles: “work” and “private”. If I have both open at the same time, they are separate browser windows with different tabs, different settings and different extentions.

I can now specify that external links open in “work”. If I now click on a link in Slack or in Thunderbird, they open up in the window with the “work” profile, even if the “private” window was the last active one.