The Swiss outfit surprised the paddock when both cars were consistently fast throughout qualifying, with Zhou Guanyu topping Q1 and eventually earning fifth place.
Bottas was as high as fourth in Q2 and then took seventh in Q3, split from his team-mate by the Ferrari of Charles Leclerc.
Alfa has been bringing new parts to the C43 on a regular basis recently, with a major floor package introduced at the last race at the British Grand Prix.
Bottas says he expected the car to be more competitive than it was at Silverstone, where neither driver made it out of the first qualifying segment, but he admitted that he was surprised by the leap up the grid.
“Based on the feeling for the car I did say coming to the weekend that it should feel a bit better than Silverstone,” said the Finn. “But it's much better. I didn't expect that, but we'll take it.
“I think we need to learn something about the new package and the set-up, and the ride heights aren’t optimised, but we're positively surprised how quick we were today, and actually in all different parts seemed to be the case.
“I think this track really brings out the good characteristics. Also normally in the straight line we seem to be a bit draggy, and here's there's only one straight. So less lap time lost there, and it’s quicker on the twisty parts.
“The team had a clean weekend, right set up direction, so everything has gone in the right direction. And then when it's about tenths to be out or in Q3, those things matter. So it was really solid day.”
Bottas started to realise that there was potential in the package in Hungary following Saturday’s FP3 session.
"After third practice when we did the lap times, I ended up 10th,” he noted. “With still an engine mode that wasn't quali mode. I knew that, okay, we're onto something here.
“So I actually told Andreas [Seidl] that it's going to be top seven today, just before quali. So a pretty good prediction. I'm sad I'm not allowed to do betting, because I could have made some good money!”
Bottas conceded that small margins can make the difference: “If you just look at the results not the lap times it looks like massive swings.
“But if you look at the lap times, it's actually not, so it is really about who gets things right on the weekend, what can change many, many positions.
“It's good to see, I think that's how F1 should be. So today, we're happy, some other teams are not.”
Additional reporting by Matt Kew
