Cofty is correct in calling evolution a "fact," because of the fact that it is a "scientific theory."
The terminology in analysis is merely different than our vernacular speech. In the scientific method when one establishes a "fact" they have what is called a "working theory," which means a validated observation. In everyday speech that is what we call a "fact."
Most of us are not scientists, and even the most analytical of among us speak in the vernacular. For instance, whereas "fact" in everyday speech is equal to "scientific theory," the everyday use of the word "theory" in science is "hypothesis."
Analytical methods use terms differently than they are employed in everyday speech. Similar to the use of the word "theory" and it's different meanings in science compared to the vernacular, critical Biblical analysis uses the word "myth" in a different way than used in everyday speaking. A critical "myth" is a story explaining how something came to be employing narrative devices, a story of origins. In everyday speech we use the word "myth" to mean a "false" report. But a critical myth is neither necessarily false nor fact, it's just a tale of the origins of this or that.
So when one speaks in the vernacular it is correct to call evidence a "fact." When speaking in scientific terms it is the "theory of evolution."