The actual infraction isn't that important (I just interpreted they meant some infraction), but what is important is that they stated the foul happened after the interception, so it could not be OPI, as that must occur after the QB throws and before the player intercepts.

Edit: I think we just took what was more important for the OPs point differently. I took the point as a penalty occurred, not a specific one. And you see it as "how could holding have happened". Which, if we are being pedantic, also wouldn't happen in the scenario you described. If it was called holding, it would have had to occur before the pass, making it not OPI. =).