NHF – new heroes for Heroes V 3.1.

The production icons for NHF have a two-pixel frame where the image touches the icon's borders, and the outline around the character itself looks thinner (although it can't be said that the thickness of the outline is equal to one). In other words, all diagonal and rounded lines depicted in pixels are essentially a jagged zigzag – therefore, in terms of width, it's not one or two pixels, but rather one and a half pixels, and it appears thinner.
In short, those two icons are executed exactly the same way as the NHF icons (including the same way as the icon shared by Dyrman).