So for this wrist grab, he's trying to twist backwards? But in what direction? Your backwards my backwards? Seems a tad vague.(and it seems to me he changed what he did from a simple block with an arm into an actuarial wrist grab again even though he abandoned that very act.) And he's using his arm to block the blade burst? I'll also add that must be the most uncomfortable wrist grab for him seeing as Taby's position means Metz's arm is inside his guard. Unless that's not a thing anymore for some reason.
Also wouldn't the path of his dagger have Tablurath's right arm still in the way? Unless he pulled his arm back before he closed the distance.
If Tab is standing roughly facing Metz (as Metz is charging his open body) then backwards would be to his right, though it's not really important as the current situation has both fighters wrestling for control, its essentially just a grapple. It wouldn't be that hard to transition from a fore-arm block to a wrist grapple after they made contact, as far as I know it's pretty standard practice for disarming.
Metz isn't really using his arm to block the blade burst, his arm just gets in the way as he's grappling because the arm is between the blade and Metz face. You have to imagine Metz still being somewhat lower than he should be because he's essentially keeping fairly low to strike low at the body, or at least was until the most recent post.
The whole movement is one action, it makes more sense if you imagine him ramming the blade upwards with his right hand while his left twists, faces Tab's and then yanks down while bending. Not that Metz really has the strength to outright overpower Tab, though he is slightly stronger I think.
I'm not sure how your character's right arm would be in the way unless we're imagining the scene differently somehow. Metz is driving his blade up immediately after his jab, which took place simultaneously to the blade exploding. (which in turn required Tab's own arm to be up away from his body)
The only way Tab's arm would be in the way would be if he completely overcame Metz strength and managed to yank his arm back like he intended in the time it took his knife to richochet and shoot upwards, which seems unlikely as Metz is the stronger.