First, it’s important to note that all the canonical appearances of the Talz (besides the episode in which they first appeared chronologically) have been after the Clone Wars. A New Hope occurs 19 years after the end of the Clone Wars, and thus at least 20 years after this episode. The other appearances of Talz are in the Princess Leia and Darth Vader comics, as well as Before the Awakening. There’s also a brief reference in Aftermath: Life Debt. All of these occur after A New Hope. As such, the appearance of Talz elsewhere in canon does not establish that they ever had space travel before "Tresspass," or even that they existed off of Ordo Plutonia.
However, two things do make it likely that there are Talz elsewhere in the galaxy:
- C-3PO can communicate with the Talz, suggesting that he’s encountered their language before.
- Even more important, Obi-Wan uses the term Talz to refer to them before he’s even able to communicate with them, suggesting that he’s familiar with the species.
This last point makes it quite likely that the Talz as a whole are no less technologically advanced than other species in the galaxy. Would Obi-Wan really know the species name of an isolated, low-tech species?
The group of Talz on the planet have been there for a long time:
OBI-WAN: It seems we’ve stumbled onto an inhabited planet.
CHO: Impossible. Our explorers have spent much time here over the long
history of Pantora. No one lives here. They’re trespassers.
OBI-WAN: With respect, Chairman Cho, these creatures, the Talz, aren’t
advanced enough to master space travel. I think they may have been
here longer than Pantora.
The Clone Wars, “Trespass”
Oddly, he speaks as if “the Talz” refers only to the group on Ordo Plutonis, despite the only reasonable way for him to know their name being his having encountered them elsewhere. But the meaning is clear: this group is incapable os space travel.
Obi-Wan suggests that the Talz may well have been the original residents of Ordo Plutonis. While he cannot be sure of this information, it fits with the general theme of the episode: the Pantorans, who claim to own the planet, are the trespassers, not the Talz.
The Databank confirms that the Talz had indeed been living on Ordo Plutonia for a long time:
Orto Plutonia had long been a protectorate of the Pantoran moon, after
Pantoran scouts searched the world and found no denizens amid its
frozen features. They had missed the Talz population, which lived
hidden in the ice canyons in villages carved out of the ice walls,
filled with huts made from animal skins pulled over bone-frames.
Presumably the Pantorans appraised the moon as having no resources of value, and thus had little interest in it. Ice planets are a dime a dozen in a universe with space travel, so it would have little scientific interest. And, as Obi-Wan says:
OBI-WAN: They only want to be left alone.
The Clone Wars, “Trespass”
It thus seems likely that the Talz were intentionally hiding from the Pantorans, which is borne out by their later asking the Pantorans to get off of their planet.
In any case, all this suggests that the Talz were long-time tenants of Ordo Plutonis, but how they arrived and lost their technology is unclear. It wouldn’t be the first instance of a spacefaring species reverting to lower technology levels, though. In Obi-Wan and Anakin, the title characters find a planet with a human population that has reverted to lower technology levels as the result of a long war. Something similar could have happened to the Talz, or some other cause could be at play, such as kidnapping, a spaceship crash, or a variety of other things.