I really think the Ru = Ur reversed, no more than that.
But where does thenium come from, that is the big question, and I haven't figured it out yet. Trouble is, it being a ST clue, I suppose it is another mistake.
yes, Ruthenium took me a while too, was trying to work out the Thenium part until finally it "twigged" with Ru being the symbol for Ruthenium as Valanne explained!