Not sure I understand "Once a Scottish court issues a Summary Order, it can be registered in an English court", that seems to deal with the issue of how a Scottish PCN is enforcement in England rather than the other way round.
I'm also not sure what they mean by a "Summary Order", whatever that may be it seems to me they still need to get a certificate of money provisions under the Civil Jurisdiction and Judgments Act 1982 in order to enforce cross-border, this works both ways (England to Scotland or Scotland to England).
I suspect the answer came from someone with an incomplete understanding of the matter.