I read somewhere that turning down money from parents is actually a sign of growing up, not disrespect. My buddy's therapist told him it's about setting boundaries and owning your own decisions, even when the offer is generous. Sounds like you handled it well, man, that's not an easy conversation to have.
Did you at least let him buy you a burger to soften the blow? My dad still thinks I live off ramen at 35, so 5k would probably come with a lecture on meal planning.