There probably is a certain amount of truth to this. I have read that long distance aerobics can hinder your strength gains in the gym. I'm pretty sure it's related to catabolic hormones that consume your tissues for energy, though I would suspect this greatly reduced in a low carber who is in ketosis. Long distance exercising below about your 70% max is effective for fat burning but not necessarily for cardiovascular training improvements. It probably is less harmful for muscle building, whereas above 70% is good for cardio improvement, but probably eats in to the lifting some.
So I guess the answer is, it depends. If you do it for a short warmup/cooldown, and not at very high intensity, you're probably okay. But if you are getting in to that cardio training zone and doing this for any more than 10 mins after a workout, you're probably sacrificing some muscle. I have also read that even if you do cardio on your days off from lifting, it can eat in to your gains.