That is just amazing, and outrageous also! Making fun of the penitent and the sin is serious.
Just a question though - was the “making fun” done in a kindly way rather than to mock? While the seal is inviolable, it is more serious to violate it to someone’s prejudice rather than advantage, such as “this dear sweet grandmother, a daily mass goer and church cleaner, confessed to me that she had forgotten to dust the top of the sacristy cabinet” would, I think, be a technical violation but hardly serious. (But I am not a canon lawyer!)
As it is in a published document (a blog) and is (potentially) serious, I think you should consider reporting it.