I don't think the other half of that comment affects my point: that the Chrome team is declining to fix bugs that only manifest on older kernels, and hence it's

I don't think the other half of that comment affects my point: that the Chrome team is declining to fix bugs that only manifest on older kernels, and hence it's reasonable to call those kernels "unsupported". I agree that it's the Chrome team's prerogative to decide that supporting those kernels is unimportant.