I believe it may outgas which is why the warning is there.
I love California, it's where I spent most of my life, but happy I don't live there any longer. lol
I'm wondering if it is the chemical used to make the lamp cord plastic flexible and pliable. I think I looked up a warning on a fan or something once and the listed carcinogen was chemical compound mixed into the electrical cord covering during the initial cord manufacturing. Just a thought...
Like has been stated above, if you use an item with a Prop 65 warning as intended, there's really no risk. Heck, those labels are often on food processing equipment (never know who's going to open them up and lick a motor)
2.2 Ball Pythons - Super Pastel (Manasa) / Banana (Foster) / Butter Bee (Pancake) / Normal (Chipit)