Interesting but prior studies in a more controlled environment show that the ability to recall a song in the correct key is only about 15%.

From the article: "Psychologists wanted to study “earworms,” the types of songs that get stuck in your head and play automatically on a loop. So they asked people to sing out any earworms they were experiencing and record them on their phones when prompted at random times throughout the day. When researchers analyzed the recordings, they found that a remarkable proportion of them perfectly matched the pitch of the original songs they were based upon.

More specifically, 44.7 percent of recordings had a pitch error of 0 semitones, and 68.9 percent were accurate within 1 semitone of the original song. These findings were recently published in the journal Attention, Perception, & Psychophysics."

This study seems extraordinarily suspect because it's essentially relying on good faith that the person recalling this song hasn't just literally heard this song on the radio a few hours before that or in the morning, and now it's an "earworm."

EDIT: The actual published paper makes it more clear how this study was done. Participants (N = 30, convenience sample) were surveyed at random times over a week and asked to produce a sung recording of any music they were experiencing in their heads. This is a little bit more reliable, but still hard to say how long this pitch perfect recall lasted from the last time that they actually heard the song.