Could this be an honest mistake?

Did you ask him why he thought that? Was his answer good? Did you tell him it had been changed 2 days ego?

I think I would find a different mechanic if you did not get a good explanation.

Most likely he was going by the sticker on the Windshield and by the mileage.

He read the sticker and thought you were mechanically useless so suggests the oil needs to be changed. It is not a visible thing on the oil...to tell the difference.If you tell him you just changed it, he will say "Oh, okay"Change the number on the sticker so you remember when you did it.Use a pen.Done.

I change oil in my car...it comes out black like paint and goes in clean like honey and in 1 day it comes out black like paint. I know the oil is changed because I kept a record of oil &filter changes. Some engines are sooty. Soot is a lubricant.

If you don't change your oil and filter every 3,000 miles there's a good chance the oil is black and dirty even though you just changed it.

Since most shops make very little money on oil changes I suspect your maintenance light was on or he saw an old oil change sticker.

You might ask him why he thought that. For example, my car electronically tracks when the oil is changed, but you have to manually tell the software that you did it. One time my mechanic forgot to do this and I got a warning from the computer a month later letting me know I was overdue for an oil change. I had to go into the system and let it know when it had been changed and set the reminder duration. So it's possible he checked the car's computer logs and saw that there was no information on the oil change and assumed it needed to be done.

You probably left the old oil sticker in the windshield and he read it.

It is possible YOU used dirty oil or only changed half of the oil.

It is also possible he read a sticker from a previous oil change and told you that based on the mileage shown, you were due for an oil change.

It is even possible that an internal leak contaminated the oil with coolant, but it isn't bad enough to be clear that is why the oil looks bad.

Probably not. An oil change call should be easy for a halfway competent mechanic. If he's not dishonest, he's inept. The oil would look dirty if it needed changing.

I wouldn't trust the guy with real mechanical problems. Good thing you found out cheaper, rather than with a transmission problem.

Did he see a sticker or some mileage information where the oil had been changed sometime in the past? If not then I would have to question this mechanic.