Who is Mathias Tumm and why is he rewarding me?

In Act I, a man named Mathias Tumm appears in the yard in front of Bernard Loredo's residence, next to the stall containing armor and weapons racks, and a large chest. I believe he first appears after:

Geralt kills the Kayran.

He acts as if Geralt has done a service for him, but I do not remember such. He gives you, at least, a recipe for Red Haze. I have confirmed this.

Why does he do this? Does Geralt meet him at any point earlier in the story?

Is he a villager you rescued from guards in the prologue perhaps? I had a similar encounter with a woman in flotsam.

He resembles Raymond Tassel, the merchant at Loredo's who tells you to get the Iron Frame for the Kayran trap. I wonder if they're supposed to be the same person. Has anyone had the Mathias Tumm encounter before meeting Raymond Tassel during the Indecent Proposal quest?

After retrieving the frame from behind Loredo's residence, Geralt's last words to Raymond are "I still need a few things, but you helped me a lot." to which he replies, "You'll find me at the market. Best of luck witcher." I don't recall seeing him anywhere after that, but I ran into Mathias the next time I went to Loredo's.