Those are two separate things.
Thresher counts a 1 attack, per the Wolfe thread.
Nothing says all the Thresher attacks are charge attacks, though.
How many models did Rassyk charge? Just one, because the rules only allow a charge to target one single model.
The only charge attack is against the model targeted with a charge, because that’s what the rules demonstrate. Absolutely nothing under Independent Model Charges says you can target and charge multiple models; every single occurrence of “target” and “model” is singular. If you could target multiple models with a charge, the rules would say that, because Warmachine rules only tell you what you can do, not every single possible thing you cannot do.
Maybe it would be helpful to frame this slightly differently, and then you’ll see why any bonuses to the Thresher rolls must be evaluated independently of one another. Here’s another example that should make this clear:
Take, for example, the legacy Khador warjack Beast-09. Beast-09 has both Thresher and Murderous. There’s a warrior model surrounded by several warjacks and an enemy structure. Beast-09 targets the warrior model with a charge and charges it. Beast opts to use Thresher.
Beast-09’s Murderous rule gives it an additional die on melee attack rolls against warrior models.
Beast-09 is charging a warrior model; it obviously gets the benefits of Murderous against the charge target because it is a warrior model, but would it get the benefit of Murderous against the non-warrior models potentially hit by its Thresher? No, because those models are not warrior models.
Likewise, only one model is targeted by a charge. Only one model can be targeted with the charge attack, by definition, because only one model can be targeted by the charge. Even if Thresher is treated as one single attack for timing purposes, only one attack is against the charge target.
(We could also easily concoct a scenario where a rule like Watcher advances a model that was an invalid charge target into range of the Thresher, and it’s pretty easy to see why an attack against such a model could not possibly be a charge attack.)