Legal adoption was not introduced in Scotland until 1930 - for any child legally adopted after this date, the original birth entry is still publicly available just like anyone else's but it is stated on the entry that the child has been adopted - it is the information in the subsequent adoption register which would tell you who that child was adopted by, and the child's adoptive name which is the information not open to the public. As this birth was prior to 1930, had the child been adopted by another family there would be no indication of that on the birth entry.Since his BC is freely available then there is no indication he was formally adopted by another family. If he had been I believe the original BC would not be publicly available.
Best wishes
Lesley