Well, there was a copper scroll included in the Dead Sea Scrolls, and repousse was used to imprint the text on that, I am not an expert in decorative motifs of the early Christians in that time period, but the pictures show a pair of what could be palm or olive branches, a starburst, in the bottom of the 3 pictures of the books might be a menorah, upper right picture seems to be a grape vine. The only thing I would wonder about was christians using a menorah symbol, but at the time they were just a sub cult of judaism so that might still be a symbol in use. The funny ‘furry cross’ on the upper left picture I honestly can’t identify, as it really is not clearly a cross, nor anything else and I can’t find it in any of my books on symbolism.
Lead was an amazingly common metal in that time period - used in coins, cooking and food storage vessels, in building as pipes and poured into stonework to bind it together. They did do repousse work on silver, gold and copper so I don’t see why someone might not do it on lead scrounged up - it was really cheap. I could see someone taking a length of discarded pipe, cutting pieces off and pounding it into a workable sheet to repousse on. I don’t see why they wouldn’t perhaps do it for a document if they didn’t have access to vellum or papyrus based paper [both of which could be expensive and most early christians were the lower end of the social spectrum in many cases] We do come across devotional inscriptions on wood, scratched on potsherds, scratched on stone and painted and embroidered on fabric.
I am somewhat interested in it being a codex instead of a scroll, the copper item in the dead sea scrolls was as i mentioned a scroll. The codex was derivative of the wax tablets used by romans, which did tend to be held together by rings so I would consider the form of the artifact plausable. Rummaging around, it does appear that christians prefer the codex form over scroll form so it is getting more and more plausible. I am just really iffy about the sheets of lead. But as I said, I can see a christian laborer using a piece of cast off lead, a good smooth rock surface, and a good smooth hammering rock and a bronze stylus to create sheets of lead and make a codex.
*the article mentions that that patina appears to date the item, but chemically speaking there are ways to patina metal so I would prefer a good forensics lab have a go at them first to confirm the age.