Picking points interactively using matplotlib

Question

I was wondering if anyone is able to explain why the artist (thisline) object is of type PathCollection, rather than of type Line2D. A working example of the problem is provided below, wherein the user is asked to click on as many points as they want, before confirming that they are happy with their selection.

import matplotlib.pyplot as plt
import numpy as np

def get_segments():
    '''
    Gets the x,y points defining the segments of the fence that the user wishes
    to investigate
    '''

    # Define a function that changes points colours when clicked and extracts the points' x,y
    def onpick(event):
        thisline = event.artist
        xdat = thisline.get_xdata()
        ydat = thisline.get_ydata()
        x_clicked.append(xdat)
        y_clicked.append(ydat)
        
        ind = event.ind
        print('x: '+str(fence_x[ind])+', y: '+str(fence_y[ind])+' clicked.')
        coll._facecolors[ind,:] = (1, 0, 0, 1)
        coll._edgecolors[ind,:] = (1, 0, 0, 1)
        fig.canvas.draw()
        
    # Make a fence
    fence_x = [1.0,1.0,2.0,2.0]
    fence_y = [1.0,2.0,2.0,1.0]

    happy = False # The user is not happy with their selection
    input_msg = 'Please click on the first and the last points of the region of the fence you are interested in'

    while not happy:

        print(input_msg)
        x_clicked = []
        y_clicked = []
    
        fig, ax = plt.subplots()
        line = ax.plot(fence_x,fence_y,'k')
        coll = ax.scatter(fence_x,fence_y,color=['blue']*len(fence_x),picker=True,pickradius=0.01)
        ax.set_aspect('equal')
        ax.set_xlabel('x(m)')
        ax.set_ylabel('y(m)')
        ax.set_title('Fence segment selector')

        fig.canvas.mpl_connect('pick_event',onpick)
        plt.show()

        print('Are you happy with your selection? (y/n):')
        happy_check = str(input())
        
        if happy_check == 'y':
            happy = True

        plt.clf()
        plt.close()

if __name__ == '__main__':
    get_segments()

Cheers