Oh no hun, it wasn't a random giveaway. ^^
You recieved it has a valentine's card. Someone sent it to you so show you appreciation, either as a friend or something else, I dunno.
It was an "event" that DeviantArt made so people could share the love.
You can read more about it here:
[link]On that time you could contribute with a work or more, by changing the deviation's classification to this: "Community Projects / Holidays / 2013 / Be My Valentine". Changing it to this would allow people to sent deviations as postcards. :3
But you can't do that now, because Valentine's Day already passed. Hoped this explained a bit. ^^