UCC28180: Wanted to know why there is requirement of Creepage slot in PCB of same track.

Hello Tapajit, 

Those slots that you have marked are not creepage slots.  There is no need for any creepage spacing here because the copper on either side of the slots are the same net.

The slots are placed there simply to direct the current flow (more specifically, the high-frequency noise currents) to favor passing to the filter capacitor pin first and then to the common-mode inductor pin rather than through solid copper to both pins at once. 

The designer of this EVM believes that this current-steering helps to improve the effectiveness of the EMI filter, based on principle.  Whether that is actually true or not, I don't know.  I don't believe that a comparison of performance with slots vs. without slots has ever been done. 

You are free to implement current-steering slots into your design, or not, as you see fit.  
These are not required by any standards agency.

Regards,
Ulrich