Krause World Coin Catalog shows the 1948 Hungarian 20 Forint (KM# 539) as being composed of .500 silver.
In relation to this coin, I don't have a problem with your findings with the ferro magnet and the neodymium magnet. The presence of 50% silver in the alloy will not affect the behaviour that you have observed.
So long as there some other magnetic metal in the .500 fine silver alloy. The strength of the magnetic attractive force will depend on the type and concentration whatever magnetic metal is in the alloy.
From your photo, the coin looks like other low silver content coins I have encountered from this era (for example, the Swedish 40% silver types). But photos sometimes don't look like the coin does in hand.
I tend to agree with @sel, but I hope you get an answer from another collector who has this coin. If you have a relationship with a jeweller or local coin store, they can also give you the answer.