I guess, it can select the wrong song, if:

• the correct song doesn’t have its acoustic fingerprint in the MusicBrainz database (otherwise it would be the closest match), and
• another song has a similar enough acoustic fingerprint, above a threshold that you can configure in the Picard settings.

I assume, it has to be a threshold, because you might have slight variations for the same song/recording, like silence at the end trimmed or volume normalized or whatever.

And yeah, Picard’s UI is certainly a bit of a hurdle. Conveying information for so many changes is definitely not easy, so I don’t want to complain.
But you know, if it would have detected that some of my songs will get renamed not just with a few capitalization fixes, but rather completely different words, and it would have prompted me for those, then I wouldn’t have misnamed songs now…