What does 'to confuse the issue' mean?

[Yulja]

English Language Proficiency Tests, Advanced Level

ESL/EFL Test #63 "Issues", question 3

As far as I'm concerned his explanation was useless as it merely ......... the issue.

(a) confused
(b) troubled
(c) disturbed
(d) upset

English Language Proficiency Tests, Advanced Level

ESL/EFL Test #63 "Issues", answer 3

As far as I'm concerned his explanation was useless as it merely confused the issue.

Correct answer: (a) confused

Your answer was: incorrect
As far as I'm concerned his explanation was useless as it merely disturbed the issue.
_________________________

It's not clear to me the meaning of the idiom "confuse the issue"? Please, could you make it more clear?

Yulja

[Conchita]

To confuse the issue is to mix everything up.