Both parameters are entered in meters.
ALT_HOLD_RTL description says something about setting another variable in meters, nothing about how itself is treated.
but it seems like meters.
That got me confused as well, first :) I think I worked it out, though:
In the table mentioned, the comment column to the right side explains the corresponding variable in the APM software, and the left column shows the actual MAVLink command to set this variable.
At least that is how I explain it to myself with my current knowledge.
Check the Configuration tab in the MissionPlanner for an example. You will see that changing a value on the right side, lets say the "P" spinner in the "Nav Roll PID", then highlights HDNG2RLL_P in the command column on the left side. That's exactly according to the table mentioned.
Plus, there is some internal multiplication going on for programming precision reasons, but don't ask me on that :) The value you enter is automatically multiplied, so I think we don't have to worry about this.
so , your conclusion is that's metric system all over ? (the only sane choice) ? :)