No, he didn't. I cannot stress enough that Griz saw Twilight as a child he had to protect, his feelings were not sexual, and while they may have become romantic somewhere along the way he had absolutely no intention to be anything but a caretaker for the sake of Twilight's development. He was obsessed with him in an unhealthy way, but he wasn't lusting after or grooming the 13-year-old. He's a weirdo, not a pedo
The bits of the past we see and hear about before they get together are filtered through Towa's self-hatred and belief that Griz hated him. That specific flashback was already explained in Chapter 9, but to summarize, Griz was overbearing and terrified of the Sacred Mark showing up and Twilight being forced into an environment where he wouldn't be able to protect him anymore, that scene was him doing the usual check, not perving on him. His expression was really intense and adult Towa misunderstood that intensity for hostility
This does make sense to me but it’s still kinda iffy how the author writes Griz as if he’s been missing and loving towa in the four years he was gone, but at that point griz only knows the 13 year old version of towa both physically and personality-wise. It could be that it was all normal love up until the moment griz saw the older towa but that doesn’t make any sense I hope I articulated well what I wanted to point out
I explained Griz and Twilight's relationship in a previous thread but I'll put a summary here: Towa's disappearance absolutely destroyed Griz in a lot of ways, and the 4 years spent in a state of severe depression and mental distress over it also had an effect on his feelings for Towa. He had sworn to protect and care for this child who didn't have anyone he could trust, only letting himself be vulnerable and cry for his mom while feverish and asleep, and in a single moment when he let stress get the better of him Griz utterly failed to keep that promise. His love got twisted into what it is now and the fact that the last thing he'd said to Twilight was "I hate you" haunted him all that time, so when Towa came back Griz was too overwhelmed by the relief and fear of making the same mistakes and losing him again that he rushed into things, by that point he was already too far gone to step back and properly consider the situation
Not gonna say he should have jerked off what he thought was a 17-year-old, and overall I think he's less mature than the preteen he was responsible for, but I at least understand where his head was at. Griz is far from a perfect guy, but he's always genuinely cared for and wanted the best for Towa
It's not clear when his feelings changed exactly, at least not in the manga, but based on what he tells Minya later it sounds like it happened at some point before Twilight's disappearance, he just refused to do anything that would jeopardize Twilight's growth and kept them hidden until now. Considering Twilight was already in a very bad environment Griz wanted to preserve as much of his childhood innocence as possible, especially since Griz was the only adult around that Twilight could rely on to take care of him
So his feelings became romantic when twilight was a kid…u keep defending him but the author made griz immediately love towa and sexually harass him by kissing him against his will as soon as he came back and he found out who he was without asking his age mind you for all he knows towa could’ve been 17 this is clearly just another Japanese author who goes by the “age of consent is 13” belief and makes grown men go after kids

Did he like him sexually as a 13??? Because I can’t seem to wrap my mind around the wording and that daydream the way he looked at him half naked???