There’s no hard evidence Rav Elyashiv actually held that, but a rabbi associated with him (who backed a conversion organization that dissolved after a disgraceful scandal) has sometimes made that claim supposedly “in his name” or something like that. Sounds like it may be his extrapolation based on what he thinks R’ Elyashiv’s views were. Anyway, even if the rabbi explicitly claimed he heard that from Rav Elyashiv’s mouth we are not obligated to believe it. There is no rule to trust every askan.
Anyway, to answer DM’s question, we don’t know if the gerus was valid at the time so we should err on the side of loving him (does that mean deleting this thread? probably), while at the same time not compromising on the truth. Think about it: if frum Jews were to befriend him, or at least treat him kindly, and speak to his heart and influence him to change his views, and he actually did so, this would be an enormous Kiddush Hashem. He needs to understand that he can engage in idealistic activism to improve the world (his biggest passion, it seems) without abandoning traditional Torah hashkafah. The same applies to other OO.