Hmm. Wiki says this: «I Love the World, also known as I Love the Whole World, is an advertising campaign launched by Discovery Channel in 2008 in promotion of their new tagline: "The World is Just... Awesome".[1] The song used in the ad is a re-writing of a traditional camping song known as I Love the Mountains or I Love the Flowers, sung to the tune of Hoagy Carmichael's 1938 "Heart & Soul", featuring a chorus of "boom-de-yadda, boom-de-yadda".[2]»
Not really confusing at all. They combined the two with the verses taking their melody from 'Heart & Soul' and the 'boom de yada' from 'I Love the Mountains.'
Upvoted for recognizing that the melody is the same as in 'Heart & Soul' but the 'boom de yada' melody is also in 'Heart & Soul' as harmony. Well, it's technically not harmony (my music theory is a little shaky) but it's in the background of the melody. Just listen to the first few measures of 'Hear & Soul' and you'll hear it.
tl:dr All parts of the mountain song melody are in 'Heart and Soul.'
Either way, the 'boom de ya da' is very catchy and nice.