I believe this is tile bleeding? I was wondering if there’s any way of fixing this within unity without needing to edit the tilesheet to add padding between tiles? I am using a newer version of unity than the tutorial author but found it strange that he is not seeing similar results in the video.
It sounds like you need to set the FilterMode on the tiles to be Point perhaps?
Select the image sheet and look in the importer.
For cute little tiles/sprites like these, I usually turn OFF compression to (Compression: None) to keep it clean, especially when you’re blowing it up pretty big onscren.