New company computer — Somehow linking my personal accounts to sites I've never logged into on a new machine?

I just started a new gig and a brand new computer, with separate iClouds, e-mails, etc. that I've only signed in with my work g-mail, is somehow recognizing my personal email when I visit sites like Pinterest (and logging me in).

I did have to put my work g-mail on my phone, and I'm wondering if that's causing the link...

Would this be resolved if I deleted the account on my phone? (I had to login to get Slack on …

accounts computer machine personal privacy