It is an output versus output occurence.
Try to print using the other PC, if it does not print, you inquiry is answered.
Just like to give you an instance though, there was this person (not me) who accidentally plugged the computer microphone plug to the speaker jack instead of the microphone jack, he was able to use the microphone, after some sessions with the microphone, he found out that the microphone produced a crackling sound then it became non-usable, it did not affect his speaker jack though.
Output ports (printer, scanner, monitor, etc. has current in it, so it will be current vs. current, hence, shorted connection.
Since you have two PC's and one printer, I presume, why not use a data switch device, both PCs are then connected to this device and you just flip a switch to select the PC that will use the printer.
After repeatedly attempting to print a document I realized that I had left the printer cable directly connected to another PC's parallel port instead of the printer. This other PC was also switched on. What are the chances of any damage being caused. Thanks for your help.