You surmised that the previous Buddhas were all born in the Indian subcontinent, simply because they had names that sounded Indian.
If you look at the excerpt from an academic paper below, certain Greek and Egyptian kings had Indian-sounding names in Emperor Ashoka's edicts, but this did not mean that they were Indian. Turamaya was Ptolemy, Maka or Maga was Magas, Alikasudara or Alikyasudala was Alexander. In fact, Greece was known as Yavana in Sanskrit (from Ionia). So, just because previous Buddhas had Indian-sounding names, it does not mean that they were Indian or that they resided in the Indian subcontinent. It only shows that they had Prakritized or Sanskritized names.
From the paper entitled "Antiochus, King of the Yavanas" by Jarl Charpentier :
As concerns Turamaya there can happily be no
doubt. That it denotes one of the Ptolemies has been
taken for granted ever since the days of Prinsep; and
it seems quite obvious that none but Ptolemy II
Philadelphus, whose long reign covered nearly four
decenniums (285-247 B.C.) , would fit into the
chronology of Asoka's reign." As for Maka or Maga
there existed, no doubt, more than one princeling of
the name of Magas; but there can be little doubt that
we hare to do here with that Magas of Cyrene whose
regnal years fall between c. 300-250 B.C. Already
Buhler(3) remarked that Amtekina (G., K.) or Amtikini
(Sh.) would rather render a Greek Avtigenes than
Avtigenes. However, although we know of at least
one Antigenes," he, for obvious reasons, cannot come
in here. The old Antigonos who met his fate at Ipsus
(301 B.C.) seems to be Out of the question; and thus
there remains only his grandson, surnamed from the
place of his birth Gonatas, whose reign extended
between 276 and 239 B.C. Finally, Alikasudara (or
Alikyasudala, K.) has long been taken to be Alexander
of Epirus(5) who was the son of Pyrrhus and
Antigone.