Not trying to be judgemental, just an observation:
In my opinion, most .arduboy files are violating license agreements. This is true even if the file was created by the original author, or with his or her blessing.
Most open source software licenses, including BSD, Apache and MIT require copyright and license related text (or at least a link) to be included even with a binary only distribution. I think GPL and LGPL also require the original source (or a way of obtaining it) to be included. I would consider a .arduboy file to be a binary distribution.
I suggest that the .arduboy guide be updated to say that a LICENSE, LICENSE.txt, LICENSE.md, LICENSE.pdf or similar file is allowed, and should be included in a .arduboy file in order to satisfy whatever license requirements apply to the other included files.
If I were creating a .arduboy file from someone else’s work, I would do this to “cover my ass” or at least as a courtesy. If not apparent, I would contact the author for clarification.
If the original author is creating a .arduboy file and uses such a license, by not including it they’re violating their own license agreement. In this case, they should consider changing the license.
As an author, I would insist that whatever license agreement I specified be followed.
It may even be desirable to make including a LICENSE file mandatory. It could possibly contain just “Public domain” or “Unknown”.