He did ask. He used the web site. There is no legal difference between using a telephone and speaking to a human, and using a website and asking a computer.
The humans will consult the computer, and he is simply talking directly to it.
No. That is not what OP says he did. He says that he entered the codes he found on the blog on the web and was rejected.
IHG then fired him.
Had he called and asked whether he could non-fraudulently use the codes he found on the blog on the Internet, we can presume that IHG would have said "no" or would have said "yes" and he would have been fine. Either way, it's not likely that IHG would have fired him.