Here's the study they reference:
https://www.ipsos.com/sites/default...10/topline_538_ipsos_post_oct_debate_poll.pdf
No matter how you plan to vote, who do you think performed best in the Democratic primary debate on Tuesday, October 15?
Base: Watched all or part of the debate Total (N=712)
Joe Biden 17
Cory Booker 4
Pete Buttigieg 15
Julian Castro 1
Tulsi Gabbard 2
Kamala Harris 5
Amy Klobuchar 6
Beto O’Rourke 3
Bernie Sanders 9
Tom Steyer 1
Elizabeth Warren 21
Andrew Yang 3
Don’t’ know/No opinion 14
Skipped -
And thinking more specifically, how would you rate the performance of each of the candidates who participated in the Democratic primary debate on Tuesday, October 15?
Joe Biden Base: Watched all or part of the debate Total (N=712)
Total Poor Performance 24
Total Good Performance 69
Pete Buttigieg Base: Watched all or part of the debate Total (N=712)
Total Poor Performance 19
Total Good Performance 66
Amy Klobuchar Base: Watched all or part of the debate Total (N=712)
Total Poor Performance 23
Total Good Performance 56
Bernie Sanders Base: Watched all or part of the debate Total (N=712)
Total Poor Performance 16
Total Good Performance 76
Elizabeth Warren Base: Watched all or part of the debate Total (N=712)
Total Poor Performance 15
Total Good Performance 78
Which of the following Democratic candidates for president are you considering voting for in the Democratic primary?
Joe Biden 57
Cory Booker 11
Pete Buttigieg 25
Julian Castro 6
Tulsi Gabbard 5
Kamala Harris 25
Amy Klobuchar 10
Beto O’Rourke 14
Bernie Sanders 39
Tom Steyer 5
Elizabeth Warren 52
Andrew Yang 11
Someone else 3
Skipped 1
I don't think their conclusion is supported by the data they reference in the first place.