Q: Can I see, how many thumbs up my deck got ?
If your deck hasn´t been in the Top 10, then yes. A thumbs up doubles your electrum reward (and rating reward I think). Normal rewards are 4/6/9/12.
Divide your gained electrum amount by the normal reward for your league, and subtract the number of wins. What you get is the number of "thumbs up".
Q: What happened ? I faced a deck with 1 HP.
Then you were lucky. The older a deck, the less HPs it has. 1 HP always remains. These 1-HP decks will either leave the top 500 quickly, or the player will put up a new deck soon. However, even a 1HP deck can win.
Q: I have won several thousands electums in one game. How ?
Top 10 get more money for their deck, and I if you defeat them, your money also increases.
(I don´t know exactly how much, now)