Le subjonctif est courant dans les subordonnées qui ont un rôle de caractérisation.

Autre exemple:

J’aimerais une voiture qui ait une belle couleur.

Dans cette phrase la couleur est ce qui importe. On fait une présupposition sur les voitures possibles.

C’est différent de:

J’aimerais une voiture qui a une belle couleur.

Ici la voiture a pu être choisie pour une autre raison, il est simplement précisé qu’elle a une belle couleur.

I do think that the kind of subjunctive in this sentence is what Glanville Price calls the generic subjunctive, which is to be found in relative clauses.

This particular type of subjunctive, as Glanville Price further explains, relates to “a possible member or members of a class.”

The member of the class of “paper,” which makes the subjunctive the appropriate choice in this context, is “[une] boulette de papier,” whose indefiniteness is only emphasized by “quelque.”

If you think I am right, please let me know by upvoting my self-answer…

Edit to add the examples from Glanville Price’s Comprehensive French Grammar:

An example will help to make this clear. If I ask someone: ‘Could
you show me the road that leads to the station?’, the relative
clause ‘that leads . . . etc.’ describes a particular road that I know (or, at any rate, that I assume) actually exists – the French
equivalent has the indicative, Pourriez-vous m’indiquer le chemin
qui conduit à la gare ? Likewise, if I say: ‘I am looking for a road
[i.e. a road that I know exists and that I am describing] that leads
to the station’, the French equivalent is: Je cherche un chemin
qui conduit à la gare. But if I ask: ‘Could you show me a road
that leads to the station?’ (i.e. I am in fact enquiring whether any
such road exists), or if I say: ‘I am looking for a road that [if such a road exists] leads to the station’, the relative clause rather than describing a particular road indicates the type of road that I want,i.e. it relates to any members of the class (which may or may not exist) of ‘roads leading to the station’. In such cases, French has the subjunctive, viz. Pourriez-vous m’indiquer un chemin qui conduise à la gare ?, or Je cherche un chemin qui conduise à la gare. Likewise, the subjunctive is of course used when the existence of the class in question is represented as hypothetical, as in ‘If you know a road that leads to the station’, Si vous connaissez un chemin qui conduise à la gare, or is denied , as in ‘There is no road that leads to the station’, Il n’y a pas de chemin qui conduise à la gare.