Great news, have you managed to talk with them about this? I saw some people created a github issue through the link I posted before but looks like they haven't been answered (at least not publicly). I remember another case where a mixer was also wrongly blacklisted by MetaMask, so I'm curious about the entire proccess.
Mixero has the option to mix Ethereum, but as far as I know, it never requires a connection to Metamask or any wallet.
How does Metamask create a blacklist at all, how do they recognize that, for example, a Bitcoin mixer is risky even though it never connects to MM.
It's a good thing that there are some warnings, but many times I came across an obvious phishing site or a fake mixer site that is out of the Metamask radar.