The tinker gnomes came from Dragonlance, by designer Jeff Grubb in particular.I'd personally be fine with the Forest Gnome being the Gnome and the tinker stuff being offloaded to a background, but I think WotC wants to accommodate the folks that want a strait up Dragonlance or World of Warcraft style Gnome.
Warcraft II: Tides of Darkness (1995) introduced tinker gnomes to Azeroth. The Warcraft creative team was into D&D and Warhammer, and you can see the influences all over the place.
Incidentally, both Richard Knaak (Dragonlance novelist) and Jeff Grubb (creator of Dragonlance's tinker gnomes) have written novels for Warcraft, both having written their first novels for the Warcraft universe in 2001: Day of the Dragon and The Last Guardian, respectively.
Jeff Grubb also was a story and lore developer for Guild Wars starting with Nightfall (the 3rd expansion), and the Asura he developed in Guild Wars: Eye of the North and Guild Wars 2 have a lot of conceptual overlap with tinker gnomes as well.