Well, 24 songs appeared in both lists. These songs were more likely to occur in the second 50 of the Hummingbird 100, and in the first 55 of the Hottest 100. That is to say - the songs we had in common were more likely to be the more popular alternative songs, which were less popular than the standard pop songs. So to speak.
Also, there were 64 artists appearing in the Hummingbird, compared to 69 in the Hottest 100 (which we should point out here, is actually 110). This equals a 64% uniqueness ratio (yes, that's the official term) for the Hummingbird, and 63% for H110 - ie, Hummingbird has a slightly higher ratio of individual artists.
Of those 64 artists, 22 were in the Hottest110 - meaning we had a much higher overlap of artists, than of songs. Which makes plenty of sense.