I don’t think the original records are on-line. PRONI may have them though. The Primary Valuation records for Divis were published in 1861. I assume you are referring to plot 5?
The Valuation Revision records which take Griffiths forward, and which are on the PRONI website, don’t show any tenant or owner of that plot up to at least 1920. (I didn’t bother checking after that). The Revision records just show 4 main plots as per the original.
Not sure what to make of that, but I don’t think checking the original records will reveal the mystery owner of plot 5.
Note that the maps are not contemporaneous with the original valuation so you do get extra plots appearing in the records which are not in the Primary Valuation, but that doesn’t appear to be the case here as plot 5 just doesn’t get a mention anywhere at all, save on the map.