This is bullshit IMO
First, take into account how many people have Yahoo saved as their homepage over Google... a LOT! Yahoo is full of crazy shit, Google is a search bar.
People go to Yahoo.com then go to mail, stocks, whatever... not all there to search. People go to Google.com to search for shit, or they go to Gmail.com for mail.
Comparing apples to apples, yes, Yahoo.com would get more daily visitors than Google.com
I can tell you from my end of looking at actual search query impressions for ad campaigns, there is less on Yahoo/Bing than on Google.. far less. This isn't for one campaign, but numerous accounts in verticals all across the board from ecomm sites, lead gen, attorneys, car dealerships, etc.
If you compare Google and their search network of sites, like AOL, Ask, etc., then Google trumps Yahoo any day of the week, but site v. site, Yahoo gets more traffic.
With that said, can they say more people search on Yahoo vs. Google? I would say not a chance