(Note: I'm atheistic agnostic.)
Firstly, describe Christian as someone who follows or believes in the teachings of Jesus Christ. Now, Jesus Christ taught compassion: feeding the poor and helping the sick.
Therefore, when you feed the poor or help the sick you are carrying out actions preached by Jesus Christ. By the definition I gave above, you're Christian. you're also Islamic and Buddhist.
You're not following/believing all that Christ taught but your actions are Christian in the same way you're Faustian if you sacrifice spiritual values for material gains. It doesn't mean you believe everything Jesus (or Faust) said.