Yes, your translation is correct.

“rien” is after “comprendre” only in tenses that aren’t composed (ex: “Je comprends rien“).

à can also be used for “comprendre“, but with “ce que” or “ce qui“, de seems correct to me.

The de is right when followed by a clause, for example. The main point of this answer is to show that A or DE, usually depends on a NOUN following ne comprendre rien à (or aux, of course) versus ne compendre rien de ce qui or ce que which introduces a RELATIVE CLAUSE.**

This answer is not about the various ways to say to express which noun comes after the A, as in “ne comprendre rien aux histoires de ma tante”; ne rien comprendre à l’histoire d’Espagne.

I understood nothing about what was said at the meeting or that was said at the meeting.

1) Je n’ai rien compris de ce qui s’est dit pendant la réunion. [Often, a reflexive verb would be used here.]

2) Je n’ai rien compris de ce qui a été dit pendant la réunion. [OK]
This is: nothing that was said at the meeting. Please note: that was said and what was said come out the same in French.

3) Je n’ai rien compris de ce qu’ils ont dit. [Versus: à leurs discours ou mots]

Comparison: /Je ne comprends rien à la mathématique/ [a noun] versus /Je ne comprends rien de ce qui [introduces a relative clause] a été dit lors de la réunion/ or /Je ne comprends rien de ce que vous dites/

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