Can I study in an English-speaking uni in Hungary for medicine and then return to USA for clinical training?

Possible, but not probable. Residency matches in the US (and other countries) are almost all reserved for students who study domestically. There are special circumstances and agreements with certain medical schools in foreign countries (read: Caribbean) but most students who study medicine in foreign countries will have to repeat classes and make special applications to get to the same level as a domestically educated student.

The English speaking Hungarian training is not USMLE approved so the answer is no.

Only if university is recognized by WHO and USA medical board.

Count on NOT getting any hospital residency position with a foreign medical degree, even if you earn an MD degree (not bachelor's degree in medicine), and are a US citizen, and pass all 3 phases of USMLE exams. No longer enough hospital residency positions for all the Americans earning MD degrees from US medical schools.