It's an interesting question whether this bus, using NG reformed via SMR, or the BEV buses in Louisville, using 87% coal-generated electricity, are dirtier. Neither makes much sense IMO - an HEV bus would seem to be cleaner. Still, this is primarily a cold-weather test of a single FCEV bus so it's no big deal that they're using H2 from SMR, unlike the Louisville fleet which will be running off coal-fired electricity for over a decade and probably a lot longer than that, as long as Senator "Coal is good for you. Here, eat some!" McConnell is representing them. It would be most useful if Flint ran an FCEV and a BEV bus side by side.
Guy [I have lots of experience designing/selling off-grid AE systems, some using EVs but don't own one. Local trips are by foot, bike and/or rapid transit].
The 'best' is the enemy of 'good enough'. Copper shot, not Silver bullets.