That article is strange. I was of the belief that most western "monospace" fonts were in fact "duospaced" under their definition. This distinction isn't apparent for normal writing, but such fonts usually make most emoji two chars wide. This is true at the very least for Adobe's "source code pro", which I typically use. It mentions the OP font as the only western example of such a font, but iA writer doesn't use integer multiples of the base width (necessary to qualify under their definition, as well as under common sense) for M and W.
IIRC it's not that monospaced fonts have double-width emoji; monospaced fonts just tend to not define glyphs for emoji at all, and instead allow the renderer to fall back for rendering of those glyphs to a non-monospaced font in the stack. This may result in emoji taking up basically-arbitrary width in text edit fields, breaking the monospacing.
Terminal emulators, however, have a model on which glyphs are always placed onto a visual grid (the PTY render-model grid, emulating text-mode VRAM); so in a terminal emulator that supports rendering Unicode at all, any glyph will have its visual width "snapped" to an integer multiple of the grid spacing, and will be considered to take up that many grid cells. It is up to the particular terminal emulator where it places the glyph within that array of grid-cells; some left-align glyphs, others center-align.
