It may be a blanket warning put on fishing tackle. I know lead has gotten a bad rap because years ago kids in cribs gnawed on wood rails painted with lead based paints and contracted lead poisoning, so now fishing tackle is required to carry the lead ingestion warning to help prevent people from chewing on jigs containing lead. I’m sure that at some point in time something was known to be a cancer causer in lab animals so n assumption was made that people ingesting that something at lab rates would get cancer too and unfortunately that something was also used, to a miniscule degree, in the process to make your line and hence the label’s warning.
A bunch of years ago sugar, the stuff you’d use on cereal, was determined to cause cancer too. Then food grilled on charcoal grills came under fire. There’s always a scare of some sort. Nicotine causes cancer, that’s proven. If the country was serious about stopping lung and other nicotine related cancers they’d stop every source of nicotine in our environment from being made available. Your Nanobraid….you are in more danger of getting a snag, braking off suddenly causing it to wrap around your neck and choke you to death.