Yup, that's exactly what happened.

Prefilling the spin on filter is discouraged, as you're filling from a non-clean source. Just oil the gasket a little bit like you would an oil filter, spin it on, and pump the primer a bit longer than you would have to if you didn't prefill. I've also read of people dumping the contents of their old fuel filter into their new one to prefill, obviously don't do that either.

You might want to order a second filter, it's good practice to carry a spare with you. Some people go for years without a filter change without issue, others have been stalled flat multiple times. I carry a spare even though I have a new tank and lines, you just never know when you're going to get a bad load of fuel. Since you just found out what kind of junk is in your fuel tank, in your situation I would DEFINITELY be carrying a spare. Carrying a spare filter can be the difference between being stuck on the side of the road for a few minutes and then on your way again, or having to get a tow.

__________________
617 swapped Toyota Pickup, 22-24 MPG, 50k miles on swap