long as it's not too tight. & I saw that too but they said that because it could stun their development & stuff but usually swaddlers are spacey at the legs. & when you use a blanket to swaddle they can get out of they want at least my baby did he would always wiggle out. he hates being swaddled now at 10 weeks tho
It's good to do however make sure his legs aren't so tight he can't move them. It can cause hip problems. But swaddle gives them the feeling so still being in the womb.