You can find other Time articles that cover their methodology, which involves paying a polling (or consulting) firm to run the poll.
> It links to several studies but not the one they're writing about.
Which one do you think is "the one they're writing about"? The Psychology Today piece opens with a description of the current state of affairs.
You might or might not have noticed that immediately after the mention of the Time poll, Psychology Today links to a survey published by the USDA finding that, among self-described vegetarians, 64% reported eating meat within the last 24 hours. Why do you doubt the Time poll?