The most common and most likely answer to this crossword clue is the 9 letter word MISJUDGES
I've seen this crossword clue in The Times
M
I
S
J
U
D
G
E
S
Buddy explains!
The straight part
We know that "Gets wrong idea about" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case gets wrong idea about = misjudges.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does MISJUDGES mean?
MISJUDGES verb- To make an error in judging, to incorrectly assess.