I definitely see why Patchface is likely the prophet of the Drowned God; he seems likely to have been a prophet even before he encountered the Drowned God when the ship went down, and went a little nuts after looking the God (demon?) in the face. I’m a little mystified by Thoros though. What did he do to draw R’hllor’s attention, and what led R’hllor to bestow his gifts on Thoros, who by all accounts was kind of a drunken lunatic before joining the Brotherhood Without Banners?

“he seems likely to have been a prophet even before he encountered the Drowned God” – how do you figure this?

As to why R’hllor worked his will by the Mummer’s Ford, I think it was a miracle. And as GRRM the recovering Catholic well knows, a miracle is cloaked in mystery and ineffable, inexplicable grace. Thoros notes that it has nothing to do with Thoros himself:

“I have no magic, child. Only prayers. That first time, his lordship had a hole right through him and blood in his mouth, I knew there was no hope. So when his poor torn chest stopped moving, I gave him the good god’s own kiss to send him on his way. I filled my mouth with fire and breathed the flames inside him, down his throat to lungs and heart and soul. The last kiss it is called, and many a time I saw the old priests bestow it on the Lord’s servants as they died. I had given it a time or two myself, as all priests must. But never before had I felt a dead man shudder as the fire filled him, nor seen his eyes come open. It was not me who raised him, my lady. It was the Lord. R’hllor is not done with him yet. Life is warmth, and warmth is fire, and fire is God’s and God’s alone.”

Now, there are some arguments that people have made that the spells and prayers that Thoros had been taught are secular magic hiding behind a religious wrapper, and that now that magic is coming back into the world, the spells are working again. (After all, the old priests never brought anyone back from the dead either.) After all, Melisandre often cloaks secular magic as reliigous in nature. 

However, I disagree. While it is possible that Thoros and Melisandre were trained in secular magic that they learned in the Red Temples as novices, Beric Dondarrion wasn’t. And yet Beric turned his blood into flame (the true version of Thoros’ old trick) without uttering a syllable or a spell, and brought Lady Stoneheart to life with a kiss that did not require filling one’s mouth with fire first. 

So I think it had nothing to do with Thoros, and solely to do with the ineffable plans of the Red God.