When a bidder places a bid the ebay system will automatically bid the minimum amount needed to put that bidder as the highest bidder.

If the amount entered by the bidder is lower than your reserve then it will bid the full amount the bidder bidded.

So... yes his maximum bid was 820. However, if he was then to bid 5250 it would only bid him 5200 as this meets your reserve and makes him the highest bidder.