That selection to path thing is neat, but have you tried Select > Border (which gives you the outermost number of pixels on the selection’s border) or the “long way”, right click the layer, Alpha to Selection, Selection > Invert, Selection > Grow, and filling the selection with a solid colour?
The first way is just like what you taught but without all the extra path steps - un-necessary and a poor choice as an example of how to use paths when Select > Border does the same in one fell swoop - and the second is a great way to do something like area lighting (fill with a bright yellow and apply a strong gaussian blur) or a drop shadow (fill it with black and offset it underneath the source layer, maybe making the layer partially opaque for a weaker shadow) or in a gif as a fade to silhouette (fill it with black and adjust the top layer’s opacity over frames to fade the object to the black fill layer) or yeah, even an outline, which I explained above and only learned better like 5 days ago and will freely admit is the wrong way to do outlines.
Although, if you have an image WITHOUT an outline that would be ruined BY an outline on its outermost pixels, you CAN do my described long way and it will preserve the image. So all methods mentioned remain valuable. 