Bart is riding by the marshal wearing a disguise. When Bart realizes the marshal recognizes him, he takes off. On the longer shot of him, he is wearing a regular hat. The next shot shows his disguise hat is back.
Bart acts as though he's never been to Denver, though that was where he performed the famous reverse swindle in "Shady Deal at Sunny Acres," during season 2. Both stories are by Roy Huggins.