IMO, that's how it works and it's not correct.
AFAIK legacy addresses can be either compressed or uncompressed and the compression is related to how the public key is represented rather than the address type.  Both compressed and uncompressed public keys can be used to generate legacy addresses that start with "1."

Both legacy and SegWit address types can accommodate compressed or uncompressed public keys.
As I see as of now on new Bitcoin wallet applications they used this "compressed public keys" by default due to their efficiency advantages, but it's not a strict rule dictated by the address type.