Kevin in ohio, either way is acceptable. The one thing I see on your welds are the craters at the end, to fix that when you are at the end of your bead instead of running off the end break the arc by going back to the way you started. Over weld can also be a defect.
I normally will leave a hard corner like that even when I plan to round it off as I did later here. I guess that is cheating but it works. I've also clamped a piece of 1/2" copper at the end of the line to basically make a puddle dam if I want a hard 90 degree end. Appreciate your insight as I have always wondered about the 2 ways of doing it.
Right now, there's probably 2 dozen guys outside with flashlights, looking at that same area on their splitter, lol. Not a bad idea, iv'e got to go and check mine right now!!!!! lol.
If He ground back to a V then he has done a full penetration weld instead of a standard fillet weld like the original. The original looked like it was not fully welded at the front and that is why it failed. Since your welder was engineered to function with only a properly executed fillet weld and you now have a full pen weld you will have no problems. Your Buddy did a professional job there! He may have been referring to 11018 rod which is an exotic big brother of 7018. It has a 110,000 tensile instead of 70,000 with 7018 but you will have no worries with the weld he did!