This is correct – at level 4, Magus (as well as other 2/3 casters) gets access to second-level spells, which is the point at which you start adding the bonus spells known you get from your Int modifier. Before level 4, when you’re adding the extra spells you get as part of levelling up, you would specifically add first-level spells.
Tangent that is not relevant to Magus
At certain levels, half-casters (like paladins and rangers) have “0” listed under spells per day, rather than “—”. For those specific types of caster, they would get spells at that level only if they get “bonus” spells from their ability modifier (so if someone was playing a paladin with a Charisma modifier of 12 or higher, they would get 1 first-level spell slot at level 4, but if they were randomly playing a paladin with a Charisma of 11 or lower, they would get 0)
(non-canom story)