Off topic, but does the $500B total global advertising spend sound wrong to anybody else? I'm seeing reports of that number, but that seems incredibly low to me

Off topic, but does the $500B total global advertising spend sound wrong to anybody else? I'm seeing reports of that number, but that seems incredibly low to me. Google made $95B in advertising revenue in 2017, can they really be almost 1/5th of the entire global advertising spend?