From the Ravenloft 3rd Edition Campaign Setting, page 40:
Tales also exist of lone monks who wander other domains. Rather than joining monasteries, these monks often learn under a single master and pass on their teachings to a single apprentice.
Hugolino's monk character could have been an Ezrite who learned from one such wandering monk, and maybe decided that the path of the monk would be his way to worship Ezra. The Church would obviously have a problem with this and he wouldn't be allowed to join the Ezrite faction, but it's a totally valid character concept.
That would work. I was thinking about it today, before I saw your post, and my idea was that his mother had been a monk in Darkon who had been forced to leave her order after conceiving a child with a Vistani in a one-night stand. So she immigrated to Borca, where her son was raised by her. He became devoted to Ezra, especially after a tragic incident later on in Barovia after which he believed he saw Ezra, but he didn't really grasp that his upbringing by his mom was abnormal and essentially monastic (of the Eastern variety). So at this point he doesn't understand in character that there is a conflict between his lifestyle and his faith.
Just an idea. Yours is a far simpler explanation and good.
OOC: My inspiration to create the character was actually seeing the PotM monk character Walter, who used his stealth and monastic speed to rescue several player corpses after a group wipe. It was so awesome, and honestly I wanted to make a character that could help others in that way. That's the OOC and non-lore relevant rationale. I'm imitating a really cool character played by a current player. I'm not sure if that's bad motivation on my part but he impressed me.
My character's devotion to Ezra resulted from my brand new character accidentally stumbling into a dark twisted plot with a DM and player, and -- when he was being sacrificed -- his previously unimportant devotion to Ezra suddenly surged, maybe as an echo of my real life religiosity. And facing a fate worse than death he turned to his formerly irrelevant deity choice for help. And the DM let him be helped by Ezra. So that was a life-changing conversion moment for my character. How cool is it for a character to meet a deity he called on for help? Especially in Ravenloft! (Though it could be a deception by the mists or dark powers of course.)
That's the whole story behind this mess.
Honestly it would be fitting, after such a divine intervention experience, for him to now be cleric rather than a monk. IC that is what I think he would do and if I could have switched his next class to cleric (multi class) I probably would have. But the rules don't allow it. And the only thing that held me back from having him remade entirely as a cleric is my OOC desire to imitate the player monk Walter. Perhaps I should just make a new character, a monk, and change my remake request to cleric.