Style originally associated with Louis Armstrong perhaps? (4)

I haven't cracked this one yet — but the brilliant team at Times for the Times have:

I think this is a reference to Ella Fitzgerald, who sang jazz in  the scat style and was associated with Louis Armstrong more than others. Or is there more to it? I didn’t think it was S (style originally) then CAT referrring to the Tin Pan Alley CATS, as that was Fats Waller not Satchmo, who AFAIK wasn’t called the cat. Discuss.