For a little more color for people unfamiliar with modern sales/marketing:
1. A user signs up to BrowserStack
2. BrowserStack (automatically) upload the submitted user’s information to Apollo
3. Apollo “enrich” the user’s details using information they already have about the person, e.g: company revenue, LinkedIn profile
4. Sales reps at BrowserStack use the enriched information to identify leads, bucket for marketing etc.
Apollo’s customer data sharing adds any information BrowserStack send to Apollo to the person’s profile with Apollo, accessible to all Apollo customers.
For example, any other Apollo customer can search something like “email addresses for decision makers at Example, Inc.” and get back a list including your email address (if you told BrowserStack you are a decision maker at Example, Inc.)
Every single marketing team is doing all of this, the only reason it was obvious in this case is that the OP used a unique email address for BrowserStack. If you sign up for any business product online, you surely have a profile in Apollo filled with details about you gathered from around the web (and details you submitted).
edit: https://www.apollo.io/privacy-policy/remove opt out link but Apollo are just one of many companies offering this service