Toybox is released under the Zero Clause BSD license (SPDX: 0BSD):
The text of the above license is included in the file LICENSE in the source.
Zero clause BSD is a public domain equivalent license.
As with CC0, unlicense, and wtfpl, the intent is to effectively place the licensed material into the public domain, which after decades of FUD (such as the time OSI's ex-lawyer compared placing code into the public domain to abandoning trash by the side of a highway) is considered somehow unsafe. But if some random third party takes public domain code and slaps some other license on it, then it's fine.
To work around this perception, the above license is a standard 2-clause BSD license minus the half sentence requiring text copied verbatim into derived works. If 2BSD is ok, the 0BSD should be ok, despite being equivalent to placing code in the public domain.
Modifying the license in this way avoids the hole android toolbox fell into where 33 copies of BSD license text were concatenated together when copyright dates changed, or the strange solution the busybox developers used to resolve tension between GPLv2's "no additional restrictions" and BSD's "you must include this large hunk of text" by sticking the two licenses at opposite ends of the file and hoping nobody noticed.