They’re not lying, they’re just attributing a sales call as a cause to some effect they only started paying attention to after the call, or they do get shaken down by a third party who targets them. Try registering a domain, your phone number on the Whois info, and the search rank shakedowns from scummy SEO services will start rolling in, calling themselves variations of “Google Search Advisors” threatening your site’s placement unless you pay. Some folks actually believe these calls are from google, and I’d expect people who own restaurants are targeted similarly, are much less techie and much less accustomed to these scams.
Then there’s also the effect of people not paying attention to their ratings in an objective way and immediately after the call start attributing any event that follows to the call.
And then of course there are folks who get a sales call after their first few reviews, as their business is picking up, and as that volume picks up some more critical folks show up and organically give negative reviews.
I don’t consider a blog post about someone who’s relaying something they say they heard from their friends to be evidence. I’d believe it if they collected data both before and after the call in an objective and consistent way.