[6] In 1906, he was described as follows: "Has only been playing in the first team for a year; makes progress every day, gets on very well with his winger, has an excellent shot, but lacks a little speed".

[6] The US Boulogne's football pitch, called the Moulin Wibert, was perched on top of a cliff, thus being both steep and exposed to all the winds.

[6] At the time, Northern France had two separate regional championships: the land and the maritime, whose winners were opposed in a final, and Boulogne therefore usually played against Dunkerque FC and its main rivals RC Calais in the maritime championship, and then only met RC Roubaix or US Tourcoing in the regional final, which they lost regularly.

[6] Basically, Boulogne, Calais, and Dunkirk played in a closed environment, so international football was far from their concerns, but his performance for the Northerners in the Paris-Nord meeting of 1908, which served as annual test matches for the French national team, convinced France's head coach, the Northerner André Billy,[6] to give him a chance in a friendly match against Switzerland in Geneva on 8 March 1908, helping his side to a 2–1 win.

[2][3][6] Mathaux, who never played in the French championship because his club was never champion of the North, earned five consecutive caps for France, losing four and not making a single goal nor assist.