Charlotte Kates of the Samidoun Palestinian Prisoner Solidarity Network told the rally outside the Vancouver Art Gallery on Friday that the attack was "heroic and brave."
Eby said the comments about the attack, that killed about 1,200 people, mostly civilians, were "the most hateful" he could imagine.
"Celebrating the murder, the rape of innocent people attending a music festival, it's awful," Eby said at an unrelated news conference on Monday.
"It's reprehensible, and it shouldn't take place in British Columbia. There is clearly an element of some individuals using an international tragedy to promote hate that's completely unacceptable."
Kates and Samidoun did not immediately respond to requests for comment.
Eby also remarked on an encampment by pro-Palestinian protesters that began at the University of B.C. on Monday.
Similar camps have appeared on campuses across the United States, as well as at McGill University in Montreal and the University of Ottawa.
At McGill, activists have set up dozens of tents. The university said Monday morning it had seen video evidence of some protesters using "unequivocally antisemitic language and intimidating behaviour" during the protest.
The UBC camp included about 20 tents on MacInnes Field by noon Monday.
Eby said a university campus, while a protected space for free speech, should foster a safe space for students of all backgrounds, especially for Jewish students during a time they feel "particularly alone on campuses and need additional support to feel safe."
"I have no reason to doubt that the leadership, both student and administration, at UBC will find that balance between ensuring students are safe and making sure that atmosphere of free exchange of ideas can continue to take place on campus."
In a series of messages posted on social media platform X, UBC protest organizers have asked supporters to bring tents and sandbags, as well as food, water, first aid and generators.
Naisha Khan, a spokeswoman for the protest camp, said tents started going up at 5 a.m. Monday, with attendees from UBC, Simon Fraser University and Emily Carr University of Art and Design.
Khan said they wouldn't leave until UBC supported the Palestinian right to "resistance," and the right of return to what is now Israel.
In a written response, UBC spokesman Matthew Ramsey said the school is monitoring the situation and keeping in contact with the RCMP.
Protests must "be taken with respect for others and within the boundaries of university policy and the law," he said.
"We also remind everyone that hate and intolerance have no place at UBC," Ramsey said. "The university must be a place of reasoned debate where conflicting views can peacefully coexist."
Before Eby, the Vancouver Art Gallery rally had drawn condemnation from Vancouver Mayor Ken Sim, who called it a "celebration of terrorism and antisemitism."
Sim said in a post on X on Sunday that people who "spew this vile hatred" were not welcome in the city.
Liberal member for Vancouver Granville Taleeb Noormohamed said on X that "glorifying Oct. 7 is unacceptable" and "does nothing to promote peace," while B.C. Opposition Leader Kevin Falcon called the speech a "celebration of the heinous murder of Jews."
