Very mysterious - perhaps they intend using 22ks from Monday and this was some sort of Health & Safety double check as it is probably some time since these units operated on the line. Alternately could have been a timing trial although this would be a bit pointless given that the new dis-improved service commences in a few days time.
Since when have Irish Rail done things is a logical order...
From a cost point of view would it not make more sense to keep the 2800 on the route over an 22. Its more less a double in capacity.