Why is "vais surfer" marked incorrect? Most sites say the two phrases are interchangeable.

Question

KwizbotLe samedi, je fais du surf avec mon frère.YouLe samedi, je vais surfer avec mon frère.

Accepted Answer

Hi Gilberts, 
We have added -
je surfe 
to the possibilities but 
je vais surfer 
is wrong as it changes the sentence to -
I go and surf or I am going to surf
Bonne Continuation !

Answer

Hi Gilberts,https://progress.lawlessfrench.com/revision/grammar/conjugate-faire-je-fais-tu-fais-vous-faites-in-le-present-present-tense"Le samedi"   --  every Saturday this is an habitual action.The future proche suggests an action to happen in the near future "je vais surfer..." but the action happens (habitually) every Saturday, not planned as a future event.This is how I see it.Jim