It's certainly a derogatory remark characterizing a runner who doesn't appeal to their standards. Whether it would be any runner slower than them or an image of runners they don’t like (e.g., fluid belts, visors, long tights, etc.) is open for debate.
I've been running for decades and the ones I see using that term are generally younger runners (i.e., young bucks), who race/train shirtless a lot, wear slick, expensive sunglasses and ultra short distance shorts, wear a man bun if they have long hair, and may sport a few tattoos. 😎
These dudes walk the walk & talk & talk....😁😉🤗