Guillain-Barré Has been known for a long time, tends to appear suddenly and whatever triggers it often can’t be identified. A generalist might consider it rare, but amongst the conditions seen by neurologists I suspect they’d think of it as serious, but merely uncommon. A friend and former neighbor of mine survived it. Andy Griffith famously was partially paralyzed by it in ‘83 for months, but recovered well to live another 24 years. It tends to get better on its own, so merely supportative treatment might save lives. I’m not up to speed, but would presume modern, more active treatment, speeds and increases recovery. So the diagnosis could be plausible.
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Today, the FDA is announcing revisions to the vaccine recipient and vaccination provider fact sheets for the Johnson & Johnson (Janssen) COVID-19 Vaccine to include information pertaining to an observed increased risk of Guillain-Barré Syndrome (GBS) following vaccination.
https://www.fda.gov/news-events/press-announcements/coronavirus-covid-19-update-july-13-2021
maybe he got it from sputnik covid vaccine?