The ABB S401M-C16NP is a single-pole SMISSLN miniature circuit breaker from the S400 family, rated 16 A with Trip Curve C and a 10 kA interrupting capacity at 240 VAC.
The three-pole S203-C10 (10 A, Curve C) shares the same SMISSLN platform and 10 kA interrupting rating, but it is a different animal for a three-phase panel. The S401M-C16NP is the single-pole 16 A version; you cannot drop it into a slot wired for the S203-C10 without rewiring the neutral and phase distribution. Stick with the pole count and ampacity your schematic calls for.