Tkinter displays text with {}
The curly braces there are a little bit of Tcl leaking through. You have passed a Python list to set the display in this line:
display.configure(text=("Bicycle", x, "was used", a[x], "times."))This is being converted into a Tcl list when applied to the Tk widget and in Tcl a list element with a space in it gets shown with curly brace quoting.
As pointed out by @jonrsharpe you should set the label text to be a string to avoid this.