more likely that he was reflecting on the fact that it’s owner told him that one of his rings would cause his downfall. Also likely reflecting on the fact that he was holding the hammer that crafted the Simarils. The theft of which led to his master Morgoth’s downfall & how uniquely ironic it would be for him to use a such a hammer to craft a ring intended to rule middle earth; only to have it ruin him.

the one ring wasn’t created last episode. It’s only created after all others are created & after Celebrimbor realizes his treachery. Kind of a necessity that to create a master ring, all the rings it dominates be in existence before it can be imbued with said power. & he crafts that one alone in mount doom.