Mullvad has a small number of well targeted ads in my experience.
If the person above frequents certain torrent trackers, reads Torrent Freak, or travels in other small VPN adjacent circles then it's no stretch to imagine they have seen Mullvad mentioned a great deal, both through ads and through unsponsered forum members ranking Mullvad high on their HOWTO safely do {X} guides.
Thinking outside the uBlock box most of the Mullvad advertorial placement I see is from Best VPNs for the coming Dystopia articles and host forum site banners (not on typical ad black lists), fellow user guides, etc.
So, not Mullvad ads being blocked but actual Mullvad themed content positioned as of direct interest to the target demographic.
If the person above frequents certain torrent trackers, reads Torrent Freak, or travels in other small VPN adjacent circles then it's no stretch to imagine they have seen Mullvad mentioned a great deal, both through ads and through unsponsered forum members ranking Mullvad high on their HOWTO safely do {X} guides.