I wouldn't say that it was speculation that did him in necessarily, but hubris.
There's ways to be speculative without being a retard.
"Here is what X thinks, here is what this person thinks, here is what I think and here are the reasons why".
He claimed to want to do this, claimed to want to "present all sides", but he did not do that.
His hubris was that, by virtue of being a popular "youtube christorian", he knew more than the people of this forum about Chris or the evolving situation.
He inserted himself into Christory, secretly, and surrounded himself with or tried to insert himself into the lives of people very partial to Chris (the Watchmen, Sockness, and Sean Walker).
When Bellagate happened, his hubris surfaced itself again, making him very, very vulnerable to being manipulated.
"I don't care what these forum people know, I have an insider source (who would turn out to be Sean Walker, unknown to him at the time) who is feeding me information that I can trust, fuck these random internet forum people".
Maybe GiBi shouldn't have gotten so close to people so close to Chris. Maybe anyone with half a brain would realize that information from these people would be compromised due to conflict of interest? But not GiBi, not with his hubris.
Now you can be speculative without fucking up, but he choose not to do this, even while repeatedly being warned not to. There was misinformation, unconfirmed things going on, and a relative amount of unknowns. I say relative, because by the time he had come in, ILJ was somewhat identified. He did not bother to read the thread, just the first few pages where Bella was trying to pretend to be Fiona, and then just went to Sean Walker for confirmation, and also emailed ILJ- because "I'm partial to better information than these people on KF have, Ill just default to trusting the inside sources".
What happened from that was people warning him that Fiona was not ILJ, to express caution there and to actually read the thread (which he didn't bother to do), and later not to publish her phone number (which he did multiple times, and seemingly not on purpose the first time- so imo this was not a "speculation move", you don't release someones phone number unless you are confident that they are involved),
and that people were also warning him that his inside source was someone close to Bella, and likely Sean Walker, which he dismissed entirely (What does this forum know? My friend is Connor, hes totally not Sean Walker, I can just go ahead and trust what I'm familiar with, who gives a fuck about these warnings).
GiBi was way too eager to release information before other people, and way too partial to too many inside actors, and his own hubris frankly did him in more than anyone else did; especially considering it made him conceited towards people on here legitimately trying to offer him advise on not leaking Fionas information or being aware of Connor/Sean Walker.
Part 2 of all this was, GiBi started saying that the reason why he fucked up so badly was due to the forum users on here, and not himself, and when getting called out for it online on twitter or in youtube videos, doubled down, starting a really autistic fall from grave that resulted in people getting more interested in him and his discord servers getting leaked as well out of curiosity over how he related to Sean Walker,
Where people then discovered, through proxy, that he was even more of an autistic retard, also had Sockness in his server, was trying to get into the Watchmen, and basically didn't give a shit about his fans.
Tldr: It was his hubris that did him in. If, at any point, he stopped doubling down and making it worse for himself, or actually listened to people on this forum, none of this would have happened.