The thundercrash bomb was a thrown grenade that had a timed fuse, not an impact explosive.
They were not used in the exact same manner as the explosive arrows on LotC, as they were timed fuse grenades that did not explode as soon as they hit (no chance for the person being attacked to avoid the explosion), were not guaranteed to explode (As the fuse might get snuffed out, or the bomb may have been a dud or w/e as opposed to 100% perfect explosion rate from explosive arrows), had much more limited range because they were thrown instead of launched from a bow. Really, the only similarities that our explosive arrows share with this weapon is that they are both explosive weapons. There are no other similarities.
I also take care to note that hand guns and basic cannons came into existence around the same time that thundercrash bombs did. To say that a weapon significantly more advanced than a thundercrash bomb is A-ok in terms of technological development whereas a weapon that existed at the same time as a thundercrash bomb is too advanced and ruins our theme is dumb.
Regardless of whether or not this weapon existed is irrelevant. Cannons also existed historically, yet we've put a lock on that weapon. What matters is whether or not a weapon makes sense in our lore and is balanced, fun, and fair to use in Pvp (A weapon that one shots through any armor no matter what is stupid and should not exist, for example). Explosive arrows don't make sense if other (and simpler) explosive weapons aren't allowed, and explosive arrows are extremely stupid for Pvp.
Biased eye on the Dwarves? What? We're not even talking about Dwarven lore here, we're talking about explosive arrows, which anybody can make/use. I am OK with cannons existing, though I think locking cannon making to one race is dumb, but I also think that explosive arrows are stupid and should not exist.
P.S. - I like how you assume I did a quick google search whilst simultaneously quoting Wikipedia, then fail to label your source.