Yeah I'm not sold on this being a void invasion. In old lore, the void is described as a place between worlds, but in Leona's new lore, it describes what's going on as a universe scale cosmic battle between strange horrors (inhuman entities and pallid, eyeless strangers that came down the mountain) and cosmic protectors (the aspects)
What sets this apart from the void is that all of our void champs and creatures are distinctly animal in nature. Cho has six identifiable limbs and looks like a reptilian insect thing. Vel has squid/octopus tentacles. Kha is literally an insect. Rek Sai is like a.. mole rat/centipede. You can easily describe their features. When Diana was attacked by one of the monsters, "it split apart, revealing a glutinous mass of sense organs and hooked teeth." That's indescribable lovecraft horror right there. Since when are void creatures covered in eyes with gaping orifices all over their bodies? None of the void creatures melt into otherworldly tar when defeated. I will admit, purple and evolving lend itself to the void, but the rest are very different. Not to mention Kassadin and Malz became infused with purple before they left Icathia/the void, not once they left.
Maybe I'm wrong, but with the current information we have on the void, the targonian horrors don't share many similarities. Hopefully we'll get a void lore rework to either distance or unite these two ideas.