Troy Knudson said:"Apparently the insert has been used for some time without anyone (voters and staff) noticing.
"I guess it's funny in some way, but my initial reaction was more disbelief that no one had noticed."
He said election officials congratulated him "for preventing future Atascosa voters from seeing the flag mistake."
There are similarities between the flags of Texas and Chile.
They both have a big white stripe on top and a big red one on the bottom. They each have a single star in the middle of a blue field. The only difference is that the blue on the Chilean flag is only in the top left corner. And in the Texas flag, the blue runs all the way down the left side.
Janice Ruple , the elections administrator in Atascosa County, said:"I don't think it's funny," she said. "It's a serious thing."
Ms Ruple, who has held her job for three years, blamed the woman who held it before her for the flag mix-up.
But she said she had no idea how long the flag of Chile had been there before she took office. The previous elections chief couldn't be reached for comment.
"We just never caught it," Ms Ruple said.
Ms Ruple said her predecessor had been known to be creative with the ballot packages sent out to voters, putting in "extra stuff".
A copy of an insert that came with Mr Knudson's absentee ballot showed a sample ballot with mock candidates for county commissioner: "Black Jack Pershing," "Jean LaFitte" and "Davey Crockett."
According to historians in Texas and Tennessee, there's no "e" in Davy.
The ballots going out of the office now don't have anything that is unnecessary, Ms Ruple said.