That's what the whistle meant.

I must be off! Well, goodbye, brother! May God give you strength and firmness to act according to the will of your soul! Goodbye, my dear boy!" He made a low bow to Foma.

There was something feminine, caressing and soft in his farewell words and bow.

Foma also bowed low to him, bowed and remained as though petrified, standing with drooping head, his hand leaning against the table.
"Come to see me when you are in town," he asked the pilgrim, who was hastily turning the handle of the cabin door.
"I will! I will come! Goodbye! Christ save you!" When the steamer's side touched the wharf Foma came out on the deck and began to look downward into the fog.

From the steamer people were walking down the gang-planks, but Foma could not discern the pilgrim among those dark figures enveloped in the dense gloom.