A large piece of marble opus sectile flooring has also been identified, still rendered with portasanta and white marble in a chromatic alternating pattern. This currently appears as the most indicative dating element, being the typology and implementation referable to the Late Antiquity age.
does not make sense to me, as I just saw lots of opus sectile pavement from the 1st Century when I was in Italy. If true, it must be a certain pattern or type of stone. What they show in the photos matches the patterns I just saw.
And at best, any Late Antique patterns would represent the terminus ad quem while there may be many buildings from earlier.
It’s a translation problem, I’d guess.