You are correct - and I am correct.

This is why pot odds always gets confusing - because people think about it in different ways. I happen to think about pot odds in terms of percentages, because I still use the handy dandy multiply outs * 2 to equal percentage rule. You clearly think of pot odds in terms of ratios - like I said before either is fine. The tricky part is that ratios are often confusing to percentage guys, because a ratio looks like you should simply divide the numerator by the denominator to get your percentage and that is NOT the case for pot odd percentages.

You are being offered 1:5 to call - $2 into a $10 pot.

but 1:5 in percentages = 1/6 = 16.7%

that's because 1:5 means "1 to 5" NOT "1 in 5". So you are correct it is not winning $12 it is only winning $10. So for every 5 times you lose $2 you need to win $10 once to make this an even play. But even though it is $2 and $10 to figure out your pot odds in terms of PERCENTAGES (rather than ratios) it is 2/10+2 it is NOT 2/10.

I believe you are also correct about the call here being slightly +EV just basing it on pot odds as well. I didn't want to get into the heavy duty math here - I just wanted to try and explain the thought process. In the end, calling this flop bet is basically an even play (you are correct that in the long run it is actually going to make you a small profit) - I was just trying to explain why that is the case.