Would you feel any differently about the value of this bug if it affected, e.g. Google or Facebook?
People on HN seem generally to believe that for any malicious activity you could do with a bug, there's a bidding group of willing buyers somewhere on some darknet site. That's not the case. Random bugs like this may get passed around, but the bugs that command a price all fit a couple specific molds: they're things you can drop into someone's existing operational process.
A Firefox drive-by RCE has some value: many organizations are set up to actively exploit Firefox browsers. So does an iOS jailbreak: lots of people stockpile iOS jailbreaks, for malware implants and for other purposes.
An important common thread among the bugs with liquid markets is that they have a meaningful half-life: once they're burned, it still takes time to eradicate the vulnerable installations. Serverside bugs are fixed worldwide instantaneously. You can see this dynamic in how grey-market payments are tranched.
If you observe someone getting paid a much lower-than-market amount for something you can complain that the company is being cheap and likely driving away a lot of potential sellers (security researchers in this case) regardless of how happy the one person is.