I'm highly doubtful of this. If it's a 303 sound, then it's probably from a real 303.
I'll give you two reasons why I'm not doubtful
1. He used TWO different presets from phoscyon.
2. He released this track with pretend analog extmix 2b. Which sounds very similar production-wise and richard has himself admitted it was soft-synths.
Every time I head on the internet it usually ends in disaster but here goes:
There is actually an explanation of how he made the track on the aphex twin warp site by the man himself but hey don’t let that bother you!