Deliberately, as clearly evidenced by the expression on Ricky's face when he snidely says, "of course, Dear" to Lucy inquiring if he's going to "help" her. His career would've been severely damaged if Lucy were to be found out and charged with fraud. Although her defense may have been pointing the finger at Freddie Filmore's sheer stupidity (a child wouldn't have bought Lucy as an old lady!).
Nonetheless, this ep is one of my faves, despite how silly the script is. I adore Lucy and the Mertzes' musical number.
I really think Freddie Fillmore caught on right away. But since Ricky was a local celebrity, he decided to have him on his show and play a trick on Lucy.