Why or? The condition will be true only if count allMatches is 1, but I find it a bit unusual:
If allMatches is {}, the second part of the statement will still be evaluated. So, with or, count allMatches is 1 will always be evaluated. Hence, the first part allMatches is not {} or is not needed at all.
I just verified that: count of {} returns 0. Consequently, there’s no need to check for an empty list in this context, count allMatches is 1 suffices.