The forward came off the bench at Signal Iduna Park and gave Manuel Pellegrini's team a fresh impetus, equalising after Fábio Silva had put Dortmund ahead shortly after half-time.
Ruibal finished from Abde Ezzalzouli's pass following a turnover in the opposition half, but Betis' hopes of taking something from the game were short-lived. Konstantinos Karetsas restored Dortmund's lead just five minutes later to secure the points.
"The first goal came at the beginning of the second half and that hurts. The substitutions brought freshness, we managed to equalise and barely five minutes later they scored again. It's a shame because we played well enough to take something from here. That's football," Ruibal told Movistar Liga de Campeones.
The 30-year-old felt Betis had shown they could compete with one of Germany's strongest sides, even if they ultimately came away empty-handed.
"They are one of the best teams in Germany. They compete with Bayern in every competition. They play their football and press, and there are moments when you have to suffer. We know how to do that, but in the end they score goals."
Ruibal also acknowledged the contribution of goalkeeper Álvaro Valles, who made several important saves to keep Betis in the contest.
"Álvaro has made some great saves, which is what you have a goalkeeper for. It was a great match in which they put us under pressure for long periods. But that's Borussia."
Despite the disappointment, Ruibal believes Betis have already demonstrated that they belong at this level. The Spanish side had collected nine points from their opening three Champions League fixtures before their first defeat of the campaign.
"Rather than saying it, you have to demonstrate it. We are demonstrating it. We haven't taken any points, but we had nine from nine before this. Now we have to think about the next game."
His message was clear when asked what Betis must do from here.
"We have to keep giving 200 per cent. If you do that, you reap what you sow."
For Ruibal, the goal was a personal milestone after a difficult period, while his contribution offered Pellegrini another reminder of the value of his squad as Betis continue their European campaign.