I'd venture to say thats not a "hairline fracture", it's too perfectly straight up the tube and at a 90deg from the ends. The vast majority of tubes on the market today are made exactly like that one, they are bent around a mandrel/form and seam welded. When to much pressure is exerted on them, they split just like that. The only way to assure that NOT happening is to buy a tube that is cut from billet/one piece of steel like a Rhino, obviously that jacks the price up quicker tho! (And in this case, that pressure would've gone to the next weakest link and either blew out the tube/stripped the threads or burst the barrel)

I would for sure want to check your barrel over but based on that seam splitting, I'd say you are probably ok. I'd mic the barrel to assure no non-visual bulge just to assure proper seal on ANY choke used in that barrel now.

Hopefully you got lucky and I personally think ANY wad (or anyther component) that doesn't work with ported/slotted barrels or tubes in todays market is just flat out stupid marketing! The VAST majority of aftermarket tubes are ported/slotted for a multitude of reasons!