He may be counting waving his hand over someones head. I agree no way the full process. You click the clink near the start of the story and it goes to the Daily Mail article. Much more information.
He may be crazy or whatever but that does not mean he’s incorrect on this matter. He became ordained in 1954. That puts the events right in the middle of his career. For all we know this might be a confession.
He also may be counting prayer for groups, and praying that those suffering from demon possession may be exorcised.
However he is counting the numbers, I doubt all the counts come from one-on-one full exorcisms.