Yes, because of historical reasons, _technically_ "magistrat" refers specifically to magistrates from the judicial branch and not all judges [0]. This is surely interesting yet administrative judges do the same job of presiding over court proceedings before them and being independent from the political authorities.
Procedure is different between the two branches, but there are also differences of procedures within each branch - for instance between penal vs civil cases.
The Constitutionnal council has ruled that the independance of administrative judges is a constitutional principle in the same way as the judicial judge [1, see point 6].
[0] of course if we need to be really technical, administrative judges are magistrates see: 'Les membres des tribunaux administratifs et des cours administratives d'appel sont des magistrats [...]' https://www.legifrance.gouv.fr/codes/article_lc/LEGIARTI0000... ; but members of the Conseil d'Etat, an administrative court, are not administrative judges - they're conseillers d'Etat.
[1] https://www.conseil-constitutionnel.fr/decision/1980/80119DC...