"Sihno" likely refers to Sinnoh, the region featured in Pokémon Diamond, Pearl, and Platinum. HeartGold and SoulSilver are remakes of the original Gold and Silver games, which take place in the Johto region.
While there are some connections between the Johto and Sinnoh regions in the Pokémon lore, you cannot physically travel between them in HeartGold and SoulSilver.