Indeed, his philosophy on the nature of mathematics is closer to "discovery", as in physics, than "invention" as in arbitrary game of rules and symbols (Hilbert) or language game (Wittgenstein).
I forget who said, "If you keep asking why, eventually you end up in the mathematics department." Calling it Platonism is a misunderstanding of how physics (and chemistry, biology, and the rest) emerge from mathematical structures and relationships that are more fundamental.
Chaitin's work (including in his own opinion) moved the philosophical needle on maths towards "discovery" and away from "invention".