... two mammals which are not close relatives ...
Depends how you define "close relatives": I see a family-resemblance ...
Human & Cat.png (90.14 kB . 560x598 - viewed 23 times)
The same chemical smell can be perceived differently by different people, that will also be true of different species,
i.e. in some cases the cats smell experience is completely different from ours, even though the chemical exposure is the same.
... how and why did it originate? ...There is natural selection for plants to produce odours to attract insects & animals in order to have them disperse pollen & seeds.