Sorry, very much false. The UEFA cup rules allowed for multiple entrants from more than one city from the start - it was the major change from the Fairs Cup. Arsenal were precluded from entering that season as a result of the FA deciding it would only nominate one entry per city to UEFA in some misguided attempt to spread European football through the country.
But that was the rules, so they qualified by right. Just like the current rules allow a team finishing fourth in the league to win next seasons Champions League, or a team finishing 7th in League 2 going up in the play offs.
You might not like that those rules existed, and you might not like that the Mags won a European trophy as a result, but you can’t say that they didn’t qualify for the tournament by right.