not ethnically they were not obviously. the original romans (the descendents of the mythical romulus and remus) were ethnic romans. the people who lived in rome and central italy.
let me ask you a question - when rome fell. did all those people - gauls, thracians, greeks, hebrews, spaniards still call themselves romans? no they did not. and the reason being it was just a political affiliation not an ethnic one. it was something that was expedient at the time to call yourself, however it had no real significance beyond the superficial political affiliation and no significance in tracing historical migratory patterns.
Nobody in the late Roman Empire was thinking thet they'd want to be that kind of romans as Romulus and Remus. They were simply the citizens of the Empire they lived in - their siblings were part of the roman army, roman administration, roman clergy...even roman emperors. The former ethnicity became very volatile within the empire borders: they mainly called the second identity after the province they lived in. For sure French, Spaniard or Italians would kept calling themselves romans if they were alone surrounded by germanics, or slavics, like Romanians were. On the other hand, for sure would been not Romanians if the main Balkan population would remained romance speaker: probably would been few peoples with different designations. The migrants made the romance in Balkans to coagulate themselves within the romance designation. But they did it from the stard - the designation as "Vlachs" was an exonym(is not something peiorative in Romanian - just not used intern). The language was called "romaneste"(Romanian).