They may already have a profile on you and now that you have moved to iOS, they can better advertise using all the data they may have already gathered. As to how it all happened, that would be hard to say since these companies have found some very clever ways to make profiles of all internet users. It would also depend on how your OPSEC was before iOS.
For now, all one can do is follow the best practices even when you have to use social media for work. Be as private and secure you can, all things considered.