That in a non-defining clause?

English Grammar Tests, Elementary Level

ESL/EFL Test #156 [color=blue]“Dishware and Utensils (1)”, question 4

A flat dish, that is used to hold many different types of foods, is also called a .

(a) chopstick
(b) plate
© bowl
(d) cup

English Grammar Tests, Elementary Level

ESL/EFL Test #156 [color=blue]“Dishware and Utensils (1)”, answer 4

A flat dish, that is used to hold many different types of foods, is also called a plate.

Correct answer: (b) plate

Your answer was: [color=green]correct
[size=200]_________________________[/size]

Hello,

A “that” relative pronoun is used in the non-defining relative clause of the sentence of this Question 4. According to Author Alan Townend, “that” cannot be used in a non-defining relative clause (ESL Lesson: Relative Pronoun–Particular–
english-test.net/lessons/21/index.html
So, why does this Question 4 contradict Author Alan Townend’s note?

Thank you.

Best wishes,
Bhikkhu1991a.

Because it is in error. I have fixed the punctuation mistakes in that test now. Thanks, Bhikkhu.