For the original "$200K" bounty, it was stated that it would be paid out in bitcoin. So it's quite possible that the person or organization funding the bounty simply has some old bitcoin laying around, and it cost them next to nothing to get it initially, and it might even be difficult for them to exchange for their preferred fiat currency today. So don't think of it as "Somebody just spent $100K," think of it as "A bitcoin speculator just traded some coins that were not worth much two years ago for something that is pretty darn valuable today."
Telegram is backed by Pavel Durov who offered the $200k in non-bit ion currency too in a previous thread here.