That is not what hydrogen embrittlement is about.
Besides, simple drop forged tools are generally quench hardened, not heat treated, it's cheaper.
However, I see something interesting in the fractured steel, it is partly rusted at one fracture point, so it was cracked *before* it broke. I suppose it is possible it was fractured during manufacture when the pin was driven in...
Or it was over stressed at some point before the time it was broken..hard to guess history..
The ends of those bars are *very* hard , so they don't bend, they are always somewhat brittle, that is a necessary consequence of making them that hard. I have a snap-on bar that is broken in exactly the same place. I broke it with a 8 foor pipe,,,,,