line art - Graphical differences between Photoshop and Paint Tool Sai

Me and my friend were discussing about Paint Tool Sai and Photoshop. About the lining systems.

He claims that when you make a line using a drawing tablet, Paint Tool Sai calculates the path and draws it smoother by filling in the bumps.

The bumps are what I get when I draw a straight line in Photoshop. In photoshop for some reason, I get bumpy lines.

What are the differences? Why is Photoshop giving me bumpy lines if I draw as fast and the same as in Sai?

My drawing tablet is UGEE and his is Huion if that's any difference too. Thank you.