That study is testing the effect of tobacco use, not pure nicotine.
EDIT—why is this downvoted? The linked study does not test your claim. Tobacco smoking is a CYP1A2 inducer so it will increase caffeine metabolism, but I am not aware of any studies demonstrating that the nicotine is responsible for this. Tobacco smoke contains PAHs and PAHs are known CYP1A2 inducers:
https://www.ncbi.nlm.nih.gov/pubmed/25911656
That study is testing the effect of tobacco use, not pure nicotine.
EDIT—why is this downvoted? The linked study does not test your claim. Tobacco smoking is a CYP1A2 inducer so it will increase caffeine metabolism, but I am not aware of any studies demonstrating that the nicotine is responsible for this. Tobacco smoke contains PAHs and PAHs are known CYP1A2 inducers: https://www.ncbi.nlm.nih.gov/pubmed/25911656