only in rarest of cases will any system temp (especially a mobo sensor) would read equal to mobo temp. that is ofcourse when you are not cooling any thing other than stock and air based heat sinks.
and in anycase there is a 14C cpu packge minimum that you can also see so if anything your room temp should be less than that or at max equal to it. AMD cpu temp sensors used to carry a negative offset, which resulted in cpu reporting less temp than what it was sitting at but I think it has now been corrected. Dont know much and I digress.
all I know about CPUTIN and SYSTIN is thatthey stand for CPU Temprature INput and similarly System Temperature INput.
what exactly do they report ad where is it read from is unclear to me and I just pay attention to core temps.
I personally prefer Open Hardware Monitor and Core Temp for this. OHM has a weird bug which shows one of my temps sitting at -33C but rest all is fine.
I'll post about CPUTIN and SYSTIN as I find a crisp clear answer.