Urn would have been better, especially against those blink heroes.
Theoretically, yes. But in practice, no Blink initiator is going to get Urned before they pull off their combo. And by the time they pulled it off, disabling it would be pointless. Granted, that Medallion didn't do much for their team either, but using Urn as a "counter" to Blink Dagger just doesn't take into account how it's used by the majority of heroes.
Saving for something a little more expensive, but a little more useful? Like a Force Staff perhaps?
Having a 1000g item that can help secure kills
now is, generally speaking, better than saving for a 2000g item you're not sure you can get. In between dying, wards, and giving up farm to everyone else, sometimes you have to tighten your belt and settle for a less impactful but still useful item, rather than hold onto a bunch of useless item pieces that don't really do anything sitting in your inventory.
Example, 8 minutes in he had Basilius, 2 Branches and 350g. This is really poverty for a support. Even Naga had brown boots at least, despite having a lower GPM than him.
Brown boots at 9 minutes.
Treads at 13 minutes.
Medallion at 17 minutes.
Ghost Scepter at 27 minutes.
Sange at 47 minutes, at which point the game was over.
Was Medallion a questionable pick up? Sure. But given his item progression, I think Silencer had a pretty good idea early on that he wasn't going to get any kind of farm whatsoever and it turned out to be the right call... just a bit early. He could've gotten a Force Staff, by 23 minutes, but he couldn't have known that. And after Ghost Scepter, he spent 20 minutes buying wards and TPs.
I don't know how well he actually played, but as a support player who frequently finds himself in a position like this, I can't fault a budget pickup like Medallion at all.