so it mean ohm law is always limited by the device anyway.
No not ohms law, that stil holds but you are not taking into account all the restance in the circuit. Any power supply has an output impedance, that is like a seriese resistor. Normally this is small compaied with the load and you can ignore it. However with a heavy load, low resistance, it can be much bigger tha the load and this resistance dominates the current you can get.
A battery can blow up if you draw too much current because it heats up because you are passing current through this resistance.
I am not sure where you get this 50mA from it is not a figure I recognise on the Arduino.
Intensity is the wrong word, it is current.
I can put it to shortcut the arduino 5v, I will not measure more than 50mA ?
No, exceed current ratings and you damage electronics.