First off, of course what Jibriil (out of respect I tend to call people what they want to be called) did is objectively wrong: apostasy indeed.
Second, I agree he's immature and unstable (given his youth and track record I agree this conversion won't last) - I won't try a dime-store diagnosis at a distance but suffice it to say he's young. Having been online for 13 years I've seen this pathology play out repeatedly.
That said, there's the third point. Before one attacks him consider that in good Western Catholic moral theology there are three criteria for a mortal sin, grave matter, sufficient reflection and full consent of the will. All we can judge is the first; as for the other two literally God only knows.
Fourth, I wrote recently when OC.net members faced losing family or friends over changing churches that a former friend, someone I considered family, turned on me and lied about it three years after I made such a change, and ended up saying to me many of the things thrown at Jibriil here. Needless to say it didn't endear this person's church to me. Ironically I love that church even though I'm not a member - in spite of people like him.
Fifth, I agree with Ebor that Seeta is being bullied and brainwashed.
Sixth, isn't it interesting that Jibriil is a convert 'spiritual tourist' and Seeta IIRC a born Muslim? Isn't that the way of it much of the time? Like with RCs and Orthodox - wonderful born members offline, lots of crazies online.
Seventh, we can't control Jibriil's life but one can read his testimony and see how the failings of Christians contributed to his decision: members of true-believer splinter sects adding to this young man's confusion.
I don't think an Orthodox priest in good standing would send one of his catechumens to an RC priest for confession and absolution! Counselling perhaps. There are respected priests of that kind, fine Christians, who wouldn't try to steal prospective Orthodox or other Christian sheep. So IMO no problem, if that's what it was.
Great St Thomas More quotation, lubeltri.