Spell? Where does the teacher spell anything?
Perhaps that's how you hear the pronunciation, but that's definitely not what he's saying. He's emphasizing saying (one), but stretching out the first syllable (mora) quite a bit. The second syllable is a voiceless "i". If you're a native English speaker, I can see why you think he's saying "yiitch", but that's just your English ear interpreting his exaggerated voicing of "ichi".
His pronunciation is well within acceptable range for the context in which he's speaking. However, if you tried to pronounce it as you seem to be hearing it and spoke it that way in regular discourse--that is, if you said "yich" instead of "ichi"--a native speaker would hear the difference because invariably you'll overdo the production of "y" to a point a native Japanese would most likely not duplicate.