Once again, I shouldn't really be posting here, but I'll put it this way;
Every dwarf /can/ use magic. Most dwarf will avoid it like the plague. Dwarfs have long memories and hold grudges for a long time, because of the First Iblees War (the one that happened in lore, not Aegis), dwarves are incredibly mistrusting of mages (not druids, clerics or runesmiths - just mages and practioners of the dark arts). After centuries, only the Irongut clan still practiced magic - something they got a lot of flak for - and with it rather well known that Dwain Irongut fathered children with a divine being (an aengul) it was just assumed dwarfs couldn't use arcane magic in the first place and the Irongut clan had the ability to because of their Aengulic blood.
After centuries of indoctrination every dwarf would very much not want to use magic, very much believe only the Irongut clan has even the capability to use magic and would very much distrust and despise mages where they do exist (one of the reasons most Irongut mages keep their abilities secret). While yes - your dwarf can technically use magic, your dwarf shouldn't want to and if you pursued it without being of Irongut descent it is in the words of rittsy "basically metagaming".
[[ This is what it actually was all along... except some people bought into even IC propaganda... ]]
