Barclay telling the women they are mistaken about what they saw in his holodeck creations would be gaslighting, because we know he was getting massages from Bev & playing flirty games with Troi, which he designed for that purpose. Geordi defending himself from the accusation that he was doing similarly is not gaslighting because Leah does have the wrong assumption, as far as anyone can prove.
The computer simulation got personal with him, unprovoked. She presumed, from what she could see alone, that she'd been a play thing for him, and despite some people trying to lean into interpreting Geordi that way, it's based on nothing. If her interpretation is wrong & he's correcting it = not gaslighting.
This doesn't excuse other things he did, including being less honest than he should've been, which had he not done so, this wouldn't have gone so badly. Him saying he was offering her "friendship", is a bit more of a stretch of the truth, but it's also in the area of perceptions, on how you interpret the informality of his interactions with her. He starts the entire story out by exclaiming that at the very least they could be friends. So, it's also not a true case of him perpetuating an utter false narrative to gaslight her. Him being friendly, is a fair assessment of him too, from his perspective, her maybe seeing it as more than friendly is fair also, from hers. That's a legit difference of perception, not selling her on a falsehood imho