Then some boats from Tiberias landed near the place where the people had eaten the bread after the Lord had given thanks.
Tiberias was located diagonally across the lake. There were now boats on the shore from there. Either the sailors had spotted the crowd on the shore and sailed across the lake to try to gain money by ferrying them or they had been on the lake the night before and the strong gale had blown them in.
Note that the miracle is not described as a miracle — there are just references to the bread and the giving of thanks.