quest 2 was out then source I bought mine Christmas 2020 I assume that's why people are down voting you.

this is what I bet the answer is. I have had a customer do this exact same thing to me. they didn't know what parts they had denied the repair estimate. picked it up and told me I swapped out their CPU.

this is it. bet he ignored a phone call that was like hey your motherboard is bad gotta replace it tested it with a known working cpu and same issues repair coat $150 to 300$ depending on what new motherboard you want is. he showed up and had to leave with it them and so they assemble is as fast as possible and forgot to swap the cpu back.

work at a repair shop. random motherboard issues I'd probably put his CPU in another motherboard and or another CPU in his motherboard so I could get it diagnosed. I'd probably stop what im doing at that point and call him with repair options and prices. sometimes they don't answer and walk into to the store instead and say no i don't want it repaired but I want my computer now now now. if it's my day off someone else will have to put it back together. they might not know that I had another CPU in their case for diagnosing if it's the motherboard or cpu as it could be either.

this senerio isn't common probably had it happen to me once a year or so. the senerio is usually we gotta reassemble it and you can grab it in an hour or 2 or tomorrow when the repair person is in but sometimes people don't want to wait.

an i7-7700 instead of an i7-7700k isn't worth the hassle of this to make be make 25 to 50$ extra.

it's probably a misunderstanding or mistake and OP isn't even reaching out to them.