Google Translate is (as often!) wrong. The sentence means:

He comes back soon. / He returns soon.

The verb rentrer is conjugated at the indicatif présent.

In French as in English, the present tense may have the meaning of a near future.

• The proximity depends on the context.

“Il rentre bientôt” suggests, a priori, minutes or hours.

“Je vais au restaurant ce soir” could be said in the morning, and of course I am not already going there.

But :
“L’armistice est signé, les soldats rentrent bientôt” suggests some weeks.