Are these kinds of mistakes possible by the editor?
Of course such mistakes can happen, editors and all other people involved are actually human.
How should I contact the editor in order to get some clarifications?
Just write a polite enquiry to the editor, either as a reply to the decision e-mail or via the submission portal. Explain briefly that you think two of the reviewer reports were linked to your submission by mistake, and ask the editor to reconsider the decision, if appropriate. Do not be afraid of editors, in my experience they are reasonable people who are open to reasonable requests like yours.