I'm sure the track surface and shoes are important, but if "singlet" means the clothing he is wearing? It's really hard to believe that makes a material difference.
In a mile it could be between 1 and 7 tenths, depending on wind and and how bad the default outfit was.
And that may seem insignificant but its big margins at the elite level.
Could give a psychological boost though - a placebo effect - even if you only believe that it gives you an edge.