A lot of them thought that no sarbecoviruses had a furin cleavage site and when they were first exposed to the issue by the headlines they assigned an overly high estimate to the FCS as being evidence of human tampering.
Then other experts pointed out that isn't uncommon at all, and they all adjusted their thinking.
"Woah, that's a million to one odds, that can't be by chance!"
"No, it's actually really common, here's a pile of similar viruses with an FCS."
"Oh, nevermind."
Experts can leap to conclusions and run their mouths off just like everyone else, doesn't take some radical world-wide conspiracy that "got" to them (other than the radical conspiracy theory of "well-informed truthful information").
I don't think that there are any Sarbecoronaviruses other than SARS2 that have an FCS. This paper from 2021 supports that conclusion [1]. There are other Coronaviruses that have an FCS, but not Sarbecoronaviruses, and none of them use PRRA. Those twelve amino acids have essentially come out of nowhere.
None of the FCS in that paper are the same: RRAR, RTAR, RSVR, RVRR, RSGR, RRSRR, RRSR, RAKR, RAHR, RRKRR. There's clearly an awful lot of functional sequences that we know of that produce an FCS and uniqueness there isn't special.
You're right that I wrote sarbecoviruses when I meant beta-coronaviruses. We still don't know of any sarbecoviruses with an FCS, but MERS has an FCS and the bat beta-coronaviruses HKU4 and HKU5 have an FCS.
There of no known lineage B sarbecoviruses that have a furin cleavage site, at least not prior to SARS-COV-2. This polybasic furin cleavage site is found in various proteins from many viruses, including Betacoronavirus Embecoviruses, and the Merbecovirus. However, within the betacoronaviruses of the sarbecovirus lineage B, this type of site is unique to SARS-CoV-2. It's never been seen before.
Then other experts pointed out that isn't uncommon at all, and they all adjusted their thinking.
"Woah, that's a million to one odds, that can't be by chance!"
"No, it's actually really common, here's a pile of similar viruses with an FCS."
"Oh, nevermind."
Experts can leap to conclusions and run their mouths off just like everyone else, doesn't take some radical world-wide conspiracy that "got" to them (other than the radical conspiracy theory of "well-informed truthful information").