Welding Tips and Tricks

Today at work I messed up working on a piece for reasons I'm unsure about.
So me and a coworker are working on the same part just different jobs.
We are welding 304 SS to 304 SS. He is using Fcaw 316L and Gtaw 316L(for repairs). I on the other hand decided to use 316L Smaw cause we have a 1ij gap and it would be easier to get at with a stick rod. I welded a little bit of it before my boss noticed and told me I would have to cut out the weld because it is the wrong filler metal. I asked how 316L fcaw, 316L gtaw was different from 316L smaw and he didn't have a solid answer other than, It just is, and You should have read the welding procedure.
Which yes I should've before I started welding but, I've seen this piece being welding on with 316L for a couple days now, I figured 316L was fine. I was suppose to use 308L.

I just got a question on what is the difference between a 308 stick rod and a 316 stick rod?
Why is 316L Fcaw and 316L Gtaw fine to use on 304SS to 304SS but 316L Smaw isn't?

its not my field, but i suspect that if the welding procedure calls for 308l then both of you need to use 308l for all types of welding.
if its a non-critical repair then 308l o 316l is acceptable (and often 309 or 312 as well)

not sure how much of a difference 308 or 316 will make, but it also depends on if its structural, the application, and also if it needs to be machined later. 316 machines a little bit different from 304.