Thanks for sending both the print and the braille. Not only is there no copyright information, there is no caption of any kind. And I certainly agree that a description is needed. So what you have here is a description and dialog. I suggest using your first method. You have started with a TN in 7-5 that starts Cartoon: followed by the description. You close your TN and have the little dialog on the next line in 1-3. I think this follows all the relevant guidelines and clearly conveys the print to the reader.
The second method leaves you with Cartoon: all by itself enclosed in a TN in 7-5, which doesn't seem to serve any purpose because there is no caption. That's why I like the first method much better. It gives the reader a clear indication of which is the the text added by the transcriber and which is the actual print dialog. It shows that the print IS dialog. And of course, it tells the reader that this is a cartoon. And your description is complete, yet short and tidy. Great work.