See #43.
It might presuppose anything you want, but it ignores the tradition of the person with whom this man was conversing.
Every practicing Catholic recites (prays, if you prefer) the Nicene Creed at least every Sunday.
Therefore every practicing Catholic professes with his lips (at the very least) belief in Jesus Christ as Savior and incarnate God in front of witnesses at least once a week.
And that's the absolute bare minimum. Saying "I'm a practicing Catholic" therefore automatically implies "I believe in the Nicene Creed" which implies "I believe in Jesus Christ as savior and God".