There were tons of reasons why people quit, some didn't like it, some moved on, some did so because they thought Blizzard was letting titty grabbers run rampant, some did because they removed sexy pictures and emotes, some did because thier fav streamer started playing Final Fantasy, etc....
If Shadowlands starts with 100 subscribers and 30 leave after a month (70 active subs)and Dragonflight starts with 50 subscribers and 2 leave after a month(48 active subs) they have retained more players than the previous expansion percentage wise. That doesn't mean Dragonflight definitely has less subs as it could also mean something like Shadowlands 100-30+70 Dragonflight 80-9=71. Since we don't have actual numbers he could be correct that Blizzard is bleeding more subscribers but it could also mean subscribers have mostly leveled out and fewer people try and leave.