Latches Symbol Representation
The symbolic representation is a black-box. It is only meant to be a representation of the sub circuit (in your case an SR Latch).

Using a not symbol is a classic way of representing that an input or an output has an inverted meaning. In this case it means that !Q has an inverted meaning from Q.

Basically, the symbol should be used in conjunction with the truth table as a black-box. Don't try and draw any conclusions from it of what the underlying logic is.