In the first scene I used the Tide Turner, which only minicrits when charging. As you can see, the Caber deals normal damage. In the second scene I used the Chargin Targe, which allows to deal critical hits, and it works as intended.

The reason the caber doesn't minicrit when shield charging (even if no explosion) is because a bit of the code checks for specific weapon types.

Charge minicrits only work for tf_weapon_sword, tf_weapon_bottle and tf_weapon_wrench.