“Don’t call him a cowboy till you’ve seen him ride”

“Don’t call him a cowboy till you’ve seen him ride” means the same as “don’t judge a book by its cover.” The phrase “Don’t call him a cowboy” was the title of a 1985 song by Conway Twitty.
 
   
Texas Slang Translation
Don’t call him a cowboy, till you’ve seen him ride
Don’t judge a book by its cover  

Lyrics Playground
DON’T CALL HIM A COWBOY
Conway Twitty

Intro
So you came from New York city and you want to see the sights
You’ve heard all about those cowboys and those crazy Texas nights
I see you’ve got your eye on something leaning on the bar
But the toughest ride he’s ever had was in his foreign car

CHORUS:
So don’t call him a cowboy until you’ve seen him ride
Cause a Stetson hat and those fancy boots don’t tell ya what’s inside
No, and if he ain’t good in the saddle Lord you won’t be satisfied
So don’t call him a cowboy until you’ve seen him ride
He’s the Hollywood idea of the wild and wooly west
In his French designer blue jeans and his custom tailored vest
You think he’s the real thing but I think you oughta know
He can’t even make it through a one night rodeo
   
Wikipedia
Conway Twitty (September 1, 1933 – June 5, 1993) was one of the United States’ most successful artists of the 20th century. Twitty had the most singles (55) reach Number 1 on various national music charts. Conway Twitty’s across the board totals were greater than that of Elvis Presley, Frank Sinatra, the Beatles and Garth Brooks. Most notably known as a country music singer
(...)
Twitty was born Harold Lloyd Jenkins in the small town of Friars Point, Mississippi and named by his father after famous silent film actor, Harold Lloyd. His family moved to Helena, Arkansas when he was 10, and there he put together his first band, the “Phillips County Ramblers”. (...) He changed his name in 1957, looking at a map, he selected Conway, Arkansas and Twitty, Texas.