Pre-Blood Storm War = mainland Telara had the Vigil approved races without Bahmi or Kelari, and with humanity more united as a larger tribe. Exploration happened by the High Elves, the more exploratory race on Telara at first (with the Dwarves digging deep instead of on the surface of Telara). Other lands were likely found, and we'll see the result of this maybe in this expansion.
Pre-Ethian disaster = Kelari moving to the Isles, Mathosia starting to form, and maybe something with the Elves, if Planetouched Wilds may come out and relate to them ;). Essentially, the world's society begins to splinter, as a result of the massive war with the dragons. Exploration likely started to happen with lands to the east, but knowledge of it is likely quite ancient, because the Travel Stones were hidden then, and the continent reeling from warfare.
Pre-Shade = Mainland Telara contracts. Mathosia spreads, but only Mathosia, as an empire. The dwarves stay in their delves again, but do communicate more with Mathosians and elves. The elves (regardless of what their first land may have been) stay put in Silverwood's Overwatch Keep. The Eth become refugees and any exploration they may have done, has stopped. The Bahmi live in isloation except for their hospitality towards visitors (especially Eth, increasing the hybrid nature of their race hehe). The Kelari now live on the Isles in their own society with the spirits. Little to no exploration at this point, and the world was in a 'recovery' stage until the damn Shade happened!
Pre Fall of Port Scion = Everyone on the run. Everything screwed. Mathosia has mostly ended and is now isolated communities, with many fleeing to Port Scion. High Elves begin to change, turning towards Life magics and the Aelfwar (those who didn't join Shyla). Dwarves were locked in their delves and the horrors within them (those who didn't join Borrin). Eth joined Orphiel and start the seeds of the Defiant faction. Bahmi had to flee their lands after a vaguely-described disaster (PLEASE PLANETOUCHED WILDS). Kelari begin suffering their own disaster due to the Shade weakening Akylios' prison, and embark on their Exodus.
AKA no one is in any good shape but to head to Port Scion. Only Ascended at this point are ones like Cyril, Borrin, Shyla etc, and they lead the plan to stay at Port Scion and regroup. Orphiel is welcomed only due to Zareph's authority (and maybe his love for Asha, and the fact the Orphiel worked to have her return to Telara), and Scion only really survives for a couple years because of Orphel's magitech shields, which fell when Alsbeth did her vaguely-described sabotage. (PORT SCION ZONE PLEASE)
Pre-Current time = Society splintered into Sanctum, Meridian, and surviving communities (neutral factions) across Telara. We see clearly that this is now a world just barely holding on, let alone wanting to explore other lands.
So yes, plenty of reason to not know much about another continent. The only two real points in history to allow this would be:
1)Pre-Blood Storm War (as in thousands of years ago..)
2)Port Scion having some measure of trade with Ember Isles.. and 'Shi-Ming', whatever that is. Otherwise, trade, politics, exploration, was all on this continent. Entire other stories (even involving magitech and the Vigil!) could have taken place outside of this land.