I don't think this is a smoking gun at all, because we don't know the story of why the difference in behavior was implemented. What not-infrequently happens is that Firefox is late to add support for some new web standard, so sites gate their usage on the user agent (which indicates that they actually bothered to test on Firefox!), and then it takes time for them to get around to removing the check after Firefox adds support.
In fact it's not completely unlikely that that is what happened here. Firefox still has incomplete support for the web authentication API [1], and in particular FIDO2 devices did not work if a PIN is set until Firefox 114 - only a few months ago! I'm not sure if this could be related, but Firefox also still does not support passkeys [2], so I'm sure someone will get blamed for anti-competitive behavior for that at some point.
In fact it's not completely unlikely that that is what happened here. Firefox still has incomplete support for the web authentication API [1], and in particular FIDO2 devices did not work if a PIN is set until Firefox 114 - only a few months ago! I'm not sure if this could be related, but Firefox also still does not support passkeys [2], so I'm sure someone will get blamed for anti-competitive behavior for that at some point.
[1] https://caniuse.com/webauthn
[2] https://caniuse.com/passkeys