I noticed it was 2 red lights inside the amplifier, what does it mean?

The amp has 7 LED's in total 4 whiteLED's provide back lighting
the bi-colour LED white/ amber is the power/standby indicator (amber when amp is in standby mode)
The two red LED's are on the Phono Board and form part of the phono amplification circuit.( D1 & D2)They are NOT fault indicators and should be lit during normal operation.

And those lights could be seen, while listening music?
Perhaps they only have a function for a technician, to tell everything is all right?
An amplifier is not made to look inside, just to amplify.
Even when something is wrong, it is not wise to open electronic equipment. Be aware that although it looks harmless, inside are voltages that can harm you. And when you have electronic skills, you know you only should work when you have a service manual.