MeteoLatvia you didn't really cause a problem, it's just a good time to teach what not to do on the internet 😉
A lot of people don't think about what information they share and in a few instances they can dramatically elevate their exposure to threats. In this scenario, for instance, you might be expecting Paul to send you an invite to download a copy of some "test software" that also requires you to disable your antivirus to run. You might be more trusting of most emails claiming to be Paul based on this prior request, which dramatically lowers the difficulty for someone trying to steal your information or ransomware your computer or organization.