Flavor contributions from sodium etc. are certainly valid, if the water source is lacking. However, assumptions were made that led to an apparent mash pH of 6 according to the OP, which may or may not have some unintended effects on the recipe. Goal for mash pH based on everything I've ever seen or heard should be like 5.2-5.5, or maybe 5.6 at most as you stated. Had the soda been added after the mash instead of before, then you could get the flavor impacts (improvements?) without mash pH going so high. In the end, though, I agree, it looks like we're probably lucky and everything will turn out just fine, hopefully, unless perhaps his water is notoriously hard like Ireland, or moderately hard (like Two Rivers, Wisconsin), in which case, keep fingers crossed.