BT Sport 3 HD certainly showed the Saints v Quins game from my experience.
Normally on BT Sports at Saturday teatime there is a Bundesliga match with the programme starting at 17:15 and the match at 17:30. I normally either watch or record and I recorded it as I was watching the Swansea/Everton game on BT Sports 1 HD at the same time. I was puzzled that the German game did not start until 18:00 yesterday.
I have just watched the Bundesliga game and the recording started with the aftermath of the Saints/Harlequins game which had just finished. It then went straight to the German game which had been underway for 30 minutes. So I can confirm that the rugby game superseded the football match, not the other way round.