It is still widely used amongst devs and I use winrar myself for many, many years.
I'm a developer myself and I also use it,
The point is RAR is a proprietary file format supported only on Windows and requires commercial software, either paid for or pirated.
He's apparently using it to give away freeware. Why not use something more ubiquitous like zip or 7z? It's another one of the many red flags.
Someone raising their hand saying they use it for their Windows job is beside the point. And the fact you can get unrar for Linux
is also beside the point, so don't waste your time correcting me on that either.