Contacts Between Sites

Had a weird situation with FluentCRM/Forms. I have it installed on a client’s site, and today I noticed that there were about 600 email addresses that had been added as contacts. Most of them were emails from one of my other sites that is running FluentCRM. The only common connection is that I use the same Sendgrid account. Would FluentSMTP be importing email addresses from Sendgrid? I didn’t give proper permissions for that with Sendgrid. All API keys have sendmail enabled and that's it. I have no idea how email address contacts from one site would end up as contacts on another. Obviously, this happening is not good. Thoughts?