Well, just looking at the obvious, it says he played and won one round of a 10k in Spain a month or so ago.
What's the rule for juniors playing in adults? Someone here will know. The number is limited, isn't it? As a function of age? Seem to remember that 14 year-olds can play a very limited number. (This event in fact seems to be his third event).
I can only find 2 15 year olds in the top ~1000 (Felix Auger Aliassime and Rayane Roumane), so it wouldn't be a huge surprise if he was the youngest ranked player right now.
The only rules relating to juniors playing in adult events is that players under 14 are categorically barred from playing, unless there's something not in the rule book that I'm missing.