If a (insert centralized service here) friend tells me about a change of plans, and I know that messages with that contact were successful in the past, then plans indeed changed because it's spoof-proof so long as you didn't make friends with two accounts that end up sharing a name and so long as the sender didn't fall victim to phishing of creds.

If an email from a contact comes in, the from/sender headers can be spoofed without anyone having fallen victim yet, so maybe plans didn't really change.

Yes there are social aspects but there is also this plainly technical aspect.