Samiri is Quran is a person an not referred to a ethinic group ; you can do more research ; he is a always referred as a person in the whole conversation and was banished from the group based on this act

https://en.wikipedia.org/wiki/Samiri

There is no consensus among Islamic scholars on which, if any, of these identifications is correct.

95. “(Moses) said: ‘What then was your object, O Samiri?’”

96. “He said: ‘I perceived what they did not perceive, so I took a handful of dust from the messenger’s track, then I threw it (into the Calf); thus my self prompted me’.”

97. “(Moses) said: ‘Depart then! Verily your share (of punishment) in this life will be that you will say: ‘Touch (me) not’; and surely there is a tryst for you (in Hereafter) which never will fail, and (now) look at your god to whose worship you kept (so long); we will certainly burn it, then we will certainly scatter (the ashes of) it broadcast in the sea’.”