[NYer]

I wonder if this is the prelude to excommunication?

Hence my question as to whether or not this falls under Canon 915.

The rule of thumb is that the bishop is responsible to initially meet with the individual in private and address the issue. Apparently, this has taken place. We will have to wait to see how the bishop now handles the situation.

[fwdude]

But I thought modern Catholics just let heretic "excommunicate themselves."

I don't expect any action to come from the Church on this. To many people have the good on it.