What Nekov said.
And also, you can't ignore the fact that Tottenham put out a much weaker side than they were capable of playing, while Borussia Dortmund played pretty much full strength. In the first game especially, when Tottenham was without three of their best midfielders, without their one and only star striker (and leading scorer in the league), and with both fullbacks rotated.
Simply because those guys needed the rest, because they're caught in a much more competitive league title race. Dortmund doesn't have to worry about that as much, because their league is generally not as competitive. Barring a really wild end of the season, they'll end second place with much room to spare behind them.
None of that's to say that Dortmund isn't better than Tottenham--I think they almost certainly are. But if you've been following Tottenham at all this season, you know that the team they put out both games was most definitely not the same eleven that's currently in 2nd place. They started the game at Dortmund with only 3 of their preferred starting 11.
If anything, the weakness of the team they put out just goes to show a difference in priorities between the clubs and highlights how competitive the EPL is.