The thing you are speculating on is answered in the very first sentence of the article: "Nations like the United States and other NATO allies have given Ukraine

The thing you are speculating on is answered in the very first sentence of the article: "Nations like the United States and other NATO allies have given Ukraine their Stingers, putting the venerable human-portable surface-to-air missile to use against Soviet-designed aircraft, as it was originally designed to do. "