I tend to post a lot when my back hurts and I'm not in the shop.
This picture:
looks a bit like restored parts I store.
Media blasting makes steel items want to rust very quickly. After blasting I take them over to the sink area, spray them down with Clean & Etch, wipe them with a paper towel and then force air dry them to remove any left over phosphate.
This leaves the part similar to the grayish area that looks bare.
I've stored phosphated but bare parts for years without paint and no trace of rust.
The gray (not ashen, just slightly darker than bare steel) parts can then be painted as the phosphate holds paint very well. It also acts as a secondary protectant to the paint.
Makes me wonder if the maker of the pulley could have done a light phosphate bath as a way to clean these prior to spraying.