Another point I would like to add is that if he had changed his mind he would have noted it directly in the video. If I made something I did not like no matter what I would tell people "I do not like making games of this genre, I will try to build something else that is more of my style", but in the video he still calls his finished product a Roguelike. So, the original idea was to make a Roguelike, his final idea was still to make a Roguelike, he did not have a change of mind in this regard. The only change of mind, maybe, was that he dropped the puzzle aspect of his game which is something he mentioned early in the video, but something that he did not follow through.
You still seem to be saying that this person just picked an arbitrary label that they didn't really understand, then worked backwards to arrive at a product that they thought fit the label. That doesn't make sense to me. Something about roguelikes evidently piqued their interest, but if they were really committed to making a turn-based, tile-based RPG, they would have. They wouldn't have scrapped that design and made a twin-stick shooter instead, just because they saw that some of those are labeled "roguelike." I can't see how tighter application of that label by other developers would have prevented any genre drift by this one. They might have just gone further afield for inspiration before finding something they liked. Games create genres, not the other way around; genres are just a shorthand in how we talk about games.
Moreover, the developer could very well have made such a change without ever seeing those other games. Did you know that Diablo 1 was originally a turn-based game? It evolved into real-time combat later in development. This despite that Blizzard North explicitly cited Rogue itself as an inspiration for Diablo.
Why would they? Didn't you say it was a theme, not a genre?
To me it is. Sometimes it's useful to loosely indicate a genre, but it can really be any sort of game.
I am actually curious now, what do these people consider a game to be a dungeon-crawler? Perhaps it is something I'd like to play too.
Sure. Here you go. This is a very strict definition that largely limits the term to only the most traditional Wizardry and Dungeon Master descendants. By this definition, Might and Magic III is a dungeon crawler, but Might and Magic VI is not.
I don't really agree with the lines drawn there, but it goes to show how subjective genre labels can be.