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