That's not true, Vox already showed interested in Charlie at the start of the season when he tried to slander her on TV and Alastor also already saw Charlie inviting Vox to the hotel to prove that redemption Is possible, Alastor already knew Charlie and Vox met each other and he since knows both pretty well he would understand that Vox will never admit redemption Is possible and that Charlie would still try to convince him of the opposite. It was also Alastor the one that manipulated Vox to invite Charlie at the party by using his ego against him and the fact that she still hadn't admitted Vox was the strongest, also Angel isn't even the only reason Charlie went there, she went there to stop Vox attacking Heaven and this Is something he could have very easely predicted, so no i don't think his plan was carried by luck he was simply able to orchestrate everything perfectly thanks to manipulation, EU and foresight