Quote from the License Text File :
The Licensee may use the Sounds in combination with other sounds in music productions
(which include soundtracks of such as films, video productions, radio/TV programs or
commercials, computer games and multimedia presentations, library music), public
performances, and other reasonable musical purposes within musical compositions.
The Licensee may modify the Sounds and may use the Sounds for commercial purposes as
part of a musical compositions on with other sounds.
The Licensee MAY NOT use the Sounds in isolation as sound effects or as loops (i.e. a
sequence of musical events) or any competitive products that are sold or re-licensed to
multiple third parties.
This is perfectly covering the "fair use" and even commercial use of those samples and it's a pretty standard License Information in the Music industry that you'll find among many samples pack.
As for the "public domain" this was seriously confirm with direct communication between Chris and Origin Sound, and I had the same confirmation by mail from them. BTW, Chris updated both pack's products pages on Sonic Academy with the mention "All Samples are 100% Royalty Free." as requested before which should also gives you confidence to purchase this pack without Copyright & License issue at all.
You can get back to Origin Sound using the mails I already provided if you would like to give them feedback or discuss about the License Text file they provide with the pack, but from S.A end it can't be more transparent I think.
Hope that can help.