The intention was that Hugh had explained the situation with Lore to Worf and Riker offscreen, in between Act Two and Act Three (i.e. during the commercial break). From the Descent Part II script on this website:
But Hugh has changed from the last time Riker and Worf saw him. He
does not welcome them; his words are tinged with bitterness and
HUGH Why are you here, Commander Riker? Hasn't the crew of the
Enterprise caused enough damage already?
Off Riker and Worf's surprise...
END OF ACT TWO
STAR TREK: "Descent, Part II" - REV. 6/24/93 - ACT THREE 28.
29 INT. UNDERGROUND CAVERNS
Riker, Worf, and Hugh have moved to another part of the chamber and
are talking. Hugh has explained Lore's takeover of the Borg, and his
take on it does not sit right with Worf.
WORF You blame us -- for what has happened to the Borg?
If you watch the episode on DVD or blu ray, you can see there is a dramatic musical cue followed by a fade to black after Hugh's line "hasn't the crew of the Enterprise caused enough damage already?", indicating that a commercial break would have gone there. People who do most of their TV watching on DVD or streaming may forget these conventions, but back when these shows were mostly seen on TV with commercials, I think it tended to be understood by audiences that when there was a new scene after a commercial break, several minutes or even longer might have passed since the last scene in-universe, including updating characters on things the audience already knew.