It has umbral properties but I don't believe it's literally darkness
It isn't, but I never stated it's a nebulus cloud or something anyways. What I meant was, it really does not have any properties that'd cause anyone to assume that it's body is simply tougher than a typical, fleshy creature. At least one would have
some basis to argue that it has extra hard body, if it has lets say crystalline element properties for example. So for all intents and purposes, it's literally just a flesh blob roaming about in space.
an asteroid acting like an asteroid
Asteroid
acted like an asteroid. By existing as a "rock in space". That's what an asteroid is. It's speed is not inherent to the specification of "being an asteroid".
where exploding during a crash is one of those
May I ask if you ever simply threw a solid rock at another object? Most things, including rocks in space, actually can easily "explode", even by something as simple as throwing with your arm. For the crumbling of an object, the requirement is not that it travels at a minimum speed of whatever the relative speed of a space rock is, to our also moving earth.
And in fact, just went for a quick research on how solid asteroids/meteorites generally are. Turns out, generally speaking, they are not very hard at all that you can just simply smash them with a typical hammer.
I will remind you that the reason an asteroid moves so fast is because it likely spent an unimaginable amount of time in space being affected by the gravitational fields of countless objects and this speed is further amplified by our earth moving at about 30km/s. These meteors are not spawned by someone, and given movement with the swing of an arm.
Furthermore, we can clearly see the Abyssal Horror not only "look" at the meteor in cinematic timing. We actually get to watch it, in normal time, reacting to it. Not "failing to react to it because the meteor goes 25km/s" where you can claim cinematic timing, a proper reaction after gazing at the meteor, bringing its tentacles to parry the blow. And we know about the reaction time of the Abyssal Horror with its tentacles, it cannot even react to half broken dragoncrafts flying around like mosquitos, or react to the ice projectiles heading to it from Blue Rose Sword's PWC.
All in all, "speed" is not an inherent property of an asteroid/meteor, it does not just propel itself to that speed upon birth. In fact, the only inherent property of it is that it is a "piece of rock in space", usually softer than things you'd find on earth, thus making it easier to explode upon impact.