@zied berrima Above mentioned account is not related to Azure AD Connect installation, if this is new setup, would suggest reviewing the audit logs, which will gives the information on how this account got created/who created it/timestamp.
If the audit logs doesnt help to isolate the issue, feel free to send us an email on azcommunity [at] microsoft [dot] com referencing this issue with a subject line "ATTN:Givary", will be happy to connect with you offline to discuss and resolve this issue.
Let me know if you have any further questions, feel free to post back.