Stephen F. Austin didn't want a fight and he didn't want Texas to separate from Mexico.
But events change minds, and being locked in a Mexican dungeon for a year would probably count as a major event in most of our lives. When he returned to Texas in August of 1835 he was ready for revolution.
In November, the provisional government appointed Austin commissioner to the United States and he embarked on a recruiting/fundraising/PR swing through the US.
In January of 1836, Austin wrote home from New Orleans to his friend Gail Borden (who would later gain fame as the inventor of condensed milk.) That letter contained these lines:
"I shall preach independence all over the U.S. wherever I go. What do you think of the enclosed idea for a flag?"
The enclosure, alas, has been lost to history.
But the following appeared in the Telegraph and Texas Register (owned by Borden and his brother) on March 5, just three days after Texas declared her independence.
"The flag presented to the San Felipe company was according to the pattern proposed for the flag of Texas and of independence. The following is the device: The English Jack, showing the origin of the Anglo-Americans; thirteen stripes, representing that most of the colonists in Texas are from the United States; the star is Texas, the only State in Mexico retaining the least spark of the light of liberty; tricolor is Mexican, showing that we once belonged to that confederacy; the whole flag is historic."
The story noted that the flag was presented by Gail Borden on behalf of the ladies who made it.
That it was presented by the man to whom Austin had sent his design, to a company raised at Austin's home, is pretty good circumstantial evidence that the flag described was Austin's own design. But circumstantial is still circumstantial.
Fortunately there is a sketch in the State library, discovered in the Nacogdoches archive sometime after it was transferred there in 1877. It bears a handwritten description that is nearly identical to what Borden published in his paper.
Written on the back is, "Stephen F. Austin's design of flag."