Steam disables trading between certain regions to avoid lower-priced currencies from trading to higher-priced currencies. This is automatic on their end.
Can you clarify what region your friend lives in that wasn't able to purchase Spriter themselves, please? I can ask Valve about it. Any screenshots showing it's not for sale in their country would also be very helpful!
Another tip for the future, just in general (as there isn't an option to add a region lock warning to our Steam page) is to try gifting directly through Steam, rather than adding it to your library and sending it that way. Steam won't allow you to make the purchase for that user if trading between those regions is restricted.
Only certain country-to-country trades are restricted. Most people can globally trade copies, but it's only countries like Russia-America that have trading disabled because it's cheaper to purchase in Russia than it is in America. This is to avoid people from gaming the currency system, which might explain why you had issues giving a copy to your friend, unfortunately. We'll look into it :)