There are enough sources indicating that Goebel is leaning toward OSU to believe that where there is smoke there is fire here. OSU most likely has more than just a "slight advantage" here, and there are a lot of signals to indicate that.
Going to just an OSU camp this summer in and of itself might not be that significant except for the fact that Goebel skipped an opportunity to attend the ND Elite Camp last weekend in order to visit OSU, even though he was in South Bend just a few days earlier. It would have taken just a slight re-shuffling of his schedule to accomodate attendance at the Elite camp, which would have indicated a stronger interest in the Irish.
OSU has shown Goebel more love than the Irish as he is their #1 D prospect at this point. In some cases, this is a significant factor, e.g. Brandon Newman.
Don't forget that academics is an issue here, and Goebel's post ND visit comments talked a lot about academic issues, a little more than you normally see after a visit. It may be that the academic requirements of ND (e.g. all First Year students are required to follow a similarly structured and relatively difficult course schedule) compared to OSU (basically no academic requirements for football players except to show up at class a few times a week) may be a swing point here. As has been mentioned in this forum many times before not everyone is interested in the academic aspect of playing CFB, and if they are not, ND is not the right place for them.
ND may be in Goebel's Top 3, but at this point in time that appears to be about as promising as being in Aghayere's Top 3 when Texas is one of the other 2. In fact, it may be even less promising.