Were you trying to select objects? and you accidentally saw that the size of the architect changed? The correct way to select objects is explained here

What?
The stepsize; also known as the architect's size, is the amount of distance shifted when you move the architect by one press of the arrow keys. It determines the next point on the grid in the cardinal directions

See also: architect , site , step size

How?
To change the step size, ensure that the mouse is in the selection mode and then drag out a rectangle in an empty part of the site. The size of the architect would change accordingly and you will see the value reflected in a small box at the bottom of the information pages

Watch out!
If you accidentally drag a very small rectangle in an empty area of the site, you may think that the architect has disappeared. So don't just idly drag out a rectangle

Undo?
If you want to return back the size of hte architect to its previous size then press the slash character /

The yellow command line box would open up and you will see that slash character inside that.

Press Enter inside the command box, and the action will get undone.

There is only one level of undo. The next undo will actually revert back to the new value you had just discarded