Hammer arrestors, need to verify.
ah ha, thank you.
does that accomplish water hammer protection for the whole building or is that only designed to protect the water heater?
It would still be ideal to have them on the laundry hook ups, etc, correct?
Arrestors should be located near the valve that can cause hammer effect. However… water hammering is usually due to excessive water velocity as a result of improper plumbing design/installation. Instead of installing a million arrestors a pressure reducing valve should be installed (if there is high pressure) and or some of the plumbing redesigned. I have no idea why they installed them, if they did, at the WH. Sometimes people will install them instead of a properly sized expansion tank. Sometimes they think it will cure the hammering and it’s the proper place for them. Even [master] plumbers often install them incorrectly. Did you check the house pressure? was it a closed or open system?
No loop just closed or open 
You’re correct. Can I blame my fingers? 
I have no idea what those things are on the water heater.
No. Usually whole house hammer arrestors are located on the main risers.
Loopy fingers 
Water pressure was about 50 and im pretty sure there was a pressure regulator buried under some soil in the top right riser in the picture below. I know better than to stick my hand down a hole in TX to try and find out…
I want to say it’s an open system? Can you confirm that from the picture above? I know the difference, maybe I’ve only ever encountered open systems so i’m not sure what i’m looking for that would tell me “closed system”. I would see a check valve after the meter if it were closed, right?
That’s one place you may see the check valve.