They sell Arduino compatible boards (amongst other things) from what I gather, so yes, they would be competitors.

I was very confused when the article referred to

> Chief microcontroller rival Adafruit

Implying that Adafruit makes their own competing microcontrollers, which sure would have been news to me.

Edit: sees sibling posted at the same time. Well that would explain it.

They also sell feather and a bunch of other vaguely similar stuff and have their own "maker" ecosystem (think CircuitPython). I like Adafruit, but they are in many senses competitors to Arduino.