That article seems reasonably conclusive to me. I can see where if you were laying prone in dry grass the muzzle blast, might (as in maybe) cause a fire. But that seems very inconclusive.
So what would a reasonable person conclude from an admittedly not entirely scientific but reasonable test?
Bullets don't cause fires period. Therefore there is no reason to continue the ban.
If they think that associated items that go along with shooting do, such as hot tailpipe exhaust, then they need to investigate further and perhaps look at those activities and not pinpointing shooting.
It is apparent that bullets themselves don't cause fires which doesn't surprise me.
Quis custodiet ipsos custodes? - Juvenal