How did you determine that? As someone who also buys old computer stuff from time to time, I wouldn't say they are collectibles.
If people are collecting them, they're collectable.
Sorry, a bit cheeky but if you are regularly buying old computer hardware then you are collecting.
There is absolutely nothing wrong with it. I still have my ZX Spectrum 48k, Atari ST and the Archimedes my parent acquired when the school was dumping them for PCs.
It's a collection.
There's collectables as in over priced stuff and collectables as in what ever you like to collect.
I think the former is more useful, and the latter could be anything.
The GGP was probably thinking the former, the GP being pedantic used the latter.