See 17 CFR § 240.10b5-1 "Trading “on the basis of” material nonpublic information in insider trading cases", particularly section (b) "Awareness of material nonpublic information."
If someone anonymously posts on Twitter that Splunk is going to get acquired by Cisco and you immediately buy options, and you don’t know who this Twitter account is, then it’s speculation. Also it’s no longer non-public information if someone posts it on Twitter.
Yes, if you trade on public information, then it's not material non public information.
“insiders must be breaching a fiduciary duty owed to their corporation when they trade on or tip confidential corporate information. This stipulation almost always means that an insider cannot trade on such information and cannot tip others about it if the insider stands to gain by doing so. https://sloanreview.mit.edu/article/when-is-it-legal-to-trad...
In the case where an unrelated outsider overhears the information that’s public disclosure. And the information no longer needs to be treated by random people as non-public.
if you’re not affiliated with the company and simply overhear and trade, make enough to retain a lawyer real quick