Hmm , the irony of it all is,
Hmm , the irony of it all is, is that it is more important than ever to have the correct fluids to hand, be it oil or coolant, these days, as everything is that much more critical, especially the European cars! Look at VW's extended oil changes, can't mix more than 500ml of an ordinary oil in an emergency only, with some of their special oils etc. You really do have to carry your own as you won't find it in out of the way places. ( Here in NZ anyway.) Anyway I'm sure it will be O.K. As a former warranty person I never quite decided who were the more annoying, those who didn't bother to read their manuals,, or those who did, and sometimes the manuals have misinformation, outdated information or like yours only sufficient to cause worry but offer no real assistance.
Of course if you had distilled water it would have been better, but I'm betting your service guy knows that most people don't have distilled water lying around, even for their batteries. If you had to go out to get it you might as well buy the right stuff, except you can't because the idiot manual doesn't give you a list of acceptable products! If you have free towing then I would have used BMW's service as it is their product and their problem, if I was really worried about it.
Sounds like the tech figured the water would get you there but it wasn't worth putting the expensive stuff in for the short trip because it was likely to end up allover the road again. As a motorcyclist I appreciate that, don't need anymore slippery toxic stuff on the road thank you/