Excluding severe vulnerabilities like ones that completely pwn your machine just by connecting it to an untrusted network is not legitimate for any reasonable bug bounty program.
Of course, a company can do it (they just did!), but it shows that they don't care about security at all.
Especially if the answer is "sorry this is out of scope" rather than "while this is out of scope for our bug bounty so we can't pay you, this looks serious and we'll make sure to get a patch out ASAP".
Ethical disclosure existed before bug bounties. Someone who wants to ensure the remediation of the bug might recognize that the staff member responding to bug bounty reports is limited in their purview and might be badly trained. Upon learning that it is out of scope for the bug bounty program did the author try their security@ or another a referenced security contact?
Your characterization of this bug as one "that completely pwn your machine just by connecting it to an untrusted network" is also hyperbolic to the extreme.