Statistically, your home PC is probably a greater risk than Coinbase.
Is there proof of this?
I think that they were speaking generally...
However, Coinbase likely spends a great deal more money than many here do, for the sake of securing their computer systems. Although Coinbase may be targeted more than the average PC or whatever, they also are cognizant of that, and so they take steps to prevent having security threats, which is evidenced in part by the fact that they haven't suffered from any "hacks" to my knowledge.