A simple offline comparison which I may have to take a moment to explain to younger viewers. When I was young, there was a popular puzzle game callled a Rubik's cube, where the aim was to make all surfaces a single colour by twisting the facets of the cube. It was effectively a single player game.

Now there were several relatively simple ways to cheat the Rubik's cube. You could take it apart and put it back together again. Or remove and restick the coloured stickers on the surface. So a lot of people who claimed to have solved it actually cheated.

Now if someone came up with a cheat solution in their bedroom out of frustration, then who cares. The only person they've cheated is themselves. However, if they then boasted to their friends "I've solved the Rubik's cube. Look at my completed cube", then I'd have a problem with that since they are seeking praise and attention that they haven't earnt in the ways they are claiming.

So the same thing applies to computer games. If you hack it in your bedroom and just change stuff locally, then who cares. However if the single player game has some interconnectivity, for example, a global high score chart that you hack the way to the top of, or collectable achievements you unfairly acquired, or you post a twitch video of your amazing run without mentioning that you'd turned off collision detection for enemy shots, then yes, you cheated.