Since I used to be involved with this kind of stuff, many years ago...
For a high-profile live event like this, they almost certainly had the captioning done by a stenocaptioner, who was using a court reporter's machine with its special keyboard. They're going syllable by syllable, phoneme by phoneme, pressing several keys at once to create stenographic text -- it looks like gobbledygook to the naked eye, but they've previously programmed a computer to translate the raw output into actual English.
When it's a phrase that might come up repeatedly, they can also create a short form of that phrase - for example, instead of doing the keystrokes for "DON-ALD-[space]-TRUMP" every time, they might program their computer so that they can just keystroke "DT" and have it come out as "DONALD TRUMP."
Therefore, when a stenocaptioner makes a typo (presses one wrong key), it usually doesn't just come out as one letter being incorrect, it comes out as a few letters of gibberish... or a completely wrong word or phrase, which appears to be what happened here.
Incidentally, the best stenocaptioners have a 99.8% accuracy rate, which basically means they're incorrect on 2 words out of every 1,000 -- but since people speak about 150 words per minute, even the best stenocaptioner will have an error every 3 or 4 minutes.