Was your gnome around during the first war? If so they were probably in Gnomeregan or maybe Dalaran, they may have been aware of the conflict or completely oblivious until the news of Stormwind’s destruction.
If you want a gnome that participated in the first war, consider Sunnyglade. The town of Sunnyglade was destroyed in Warcraft 1. Only one building was left standing, a mage tower that the orc warlocks needed. That tower is (most likely) now the Tower of Azora, populated almost exclusively by gnomes. Despite the fact that it is a mage tower, it has been stated that most of the gnomes are not mages, so a gnome of any class could be from here.
Let’s take a step back, look at some simplified high level stuff, and maybe put on a tin foil hat.
When the human kingdoms were taught magic by the high elves, the mages left Strom and went north to found the city of Dalaran. The people that formed Stormwind left Strom and headed south. This might not seem like a big deal, but this southward journey is when the humans came to really know dwarves*. See that asterisk on dwarves? Anytime you have dwarves you have *(and gnomes).
I propose that human mages did not travel south to Stromwind, but along the way a group of gnomes joined up with those humans and accompanied them on their travels. These gnomes went on to teach the southern humans their techniques of arcane magic.
In founding the town of Sunnyglade, the gnomes and humans created a place dedicated to higher learning. With a reputation as a center of knowledge, the Horde decides to target it because they want more information about human magic.
The town is raised except for the tower, which is looted. The inhabitants that don’t flee or escape are captured by the horde, but soon liberated by the armies of Stormwind.
Because their is little to no information surviving about the town, there’s a lot of room for players to write themselves in.