The other possibility is that he was a non conformist and the Scotlandspeople records are mostly Church of Scotland unless the minister was kind enough to list some of his nonconformists in the parish.
The term 'non-conformist' specifically means not part of the Church of
England, and it has no relevance or meaning in relation to church denominations in Scotland. There were, and are, a bewildering number of
dissenting or
secession denominations in Scotland, besides Roman Catholics and Episcopalians.
It wasn't a case of the minister being 'kind enough' to record events affecting people in his parish but not of his congregation. The Church of Scotland was supposed, by an act of the Scottish parliament in about 15-something-or-other, to keep a record of all baptisms and marriages, regardless of which denomination the people involved belonged to. In practice, for reasons I won't go into because it would take far too long, this mostly didn't happen, though some parish clerks (it was they, not the ministers, who were responsible for keepng the parish records) were more diligent at recording than others.
Most of the surviving Scottish records of births/baptisms, banns/marriages and deaths/burials in Scotland before the start of civil registration in 1855 are available on the Scotland's People web site. The notable exception is the Episcopalian records, which have not been brought together in a single repository and are not easy to find. However the surviving records of the Church of Scotland and the Roman Catholic Church, plus the majority of the Secession and Free Churches' records, are all available.