An actual good epoxy primer should not do that. It seals. Something fishy here. BE SURE it is rust. BE SURE it was a brand name two part epoxy primer on bare metal. Any good sandblaster knows it needs primed pretty quick. Except where I live
As Robert is asking: Some people refer to all blasting as "sandblasting". Find out what was used: sand, glass, black magic, garnet, soda, walnut................etc.
If it was a redish brown "layer", it is some sort of primer.
