A person (not me) from another forum asked to humblebundle about giving aways on reddit, and this was their answer:

"Hello there,

Thank you for reaching out to us here at Humble Bundle Support with your concerns about giveaways on Reddit. I apologize if my reply via social media seemed ambiguous to you and I will do my best to clear up any confusion about this reply.

Please note that unauthorized secondary distribution of games purchased through Humble Bundle is a violation of our Terms of Service. This, unfortunately, includes the trading of game keys for other keys or reselling to other users.

When we state that items purchased via Humble Bundle are intended for personal use and limited gifting to family and friends, we are referring to personal relationships and well-known friends. One of the many reasons we recommend gifting to those that you already know is so that the gift recipient can easily get in contact with you again should there be any issues with the game key received. Sometimes gifted keys don't quite work out due to various problems and, if the key was received via trade or giveaway, we would not be able to provide support because the method in which the key was received violates our Terms of Service.

We do not condone trading or reselling keys, but gifting is perfectly fine; we typically recommend gifting to a personal friend or family member, as highlighted in our article. If you are a Humble Partner that has received a key as part of the program, those can be given or raffled away. Raffles can use Humble keys as a reward - just make sure you do not require a form of payment as an entry requirement.

It should be noted that both trading and reselling keys on the “grey market” has a negative effect on the industry’s ability to flourish and support our awesome developers. While I am very sorry to hear that this policy has had a negative impact on the Humble Bundle Reddit community, we are doing our best to mitigate the issues brought about by the trading and reselling of keys and must take action against activities that appear to be violating our Terms of Service.

This does not mean we discourage gifting or being generous, but we do ask that our users avoid purchasing or trading keys with secondary distributors and send gifts to those they are close to instead.

Again, my sincerest apologies for the upset this has caused to your community. Please let me know if you have any further concerns or questions and I'll do my best to clear them up.

All the best,

-Crystal Humble Bundle http://support.humblebundle.com/"

This is it.

Tldr: Apparently, gifting keys to strangers is OK, better to IRL friends because support (whatever). Trading and selling not OK