The speaker pronouces menu's as (men-ow's). I've only ever heard it pronounced (men-oo's)
The ending ’s (apostrophe s) is added to words ending in -a, -i, -o, -u or -y. This is necessary because otherwise the vowel length would change (think of the spelling rules):
de firma (firm) - firma’s
de taxi (taxi) - taxi’s
de auto (car) - auto’s
de paraplu (umbrella) - paraplu’s
de baby (baby) - baby’s
The audio is so wrong! "menu's" is not pronounced that way. Even Google Translate pronounces it correct.