He is genuinely an outlier for multiple things when it comes to void physiology, it would not surprise me that he would be an outlier here too, esp given his resemblance to kingmoulds which I wouldn't exactly use as counter-examples again pure void entities, at worst I would make the argument that given void seems like a fluid, it should have a corresponding solid state, which fits with the more solid look of the collector when compared to every other void being whose appearance is much more fluid and malleable compared to the collecter (See void given form, the shade using its body to form a pseudo nail to attack the knight).
In addition, given how the void appears within the dream realm (in particular the radiance fight where it has very much not just liquid properties and is far more ethereal), please do not say that it is because it is in a mental plane that it is behaving like that because we should both be aware of the fact that the dream realm is as real as, and stuff that is transferred to it, act the same way as they do outside, and to add more fuel to this fire, the whole void particles we see in areas inhabited by void that float about and pop in and out of being, like how much stuff do you want me to bring.