I misheard it too. The first pronunciation ends so abruptly that it sounds like a glottal stop: the same closure that interrupts the voice and airflow in 'uh-oh' and 'uh-uh'. The vowel length is just long enough to make me think that the speaker is trying to avoid that confusion. Since in AmE the voiceless dental stop /t/ is usually articulated as a glottal stop [ʔ] it's easy to interpret [nʌmnʌʔ] as a surface representation of /nʌmnʌt/. In order to make his interpretation clear, young Master Mishra (from West Lafayette!) makes sure to aspirate the /t/ for [nʌmnʌtʰ].
(Hat tip Jon)