A full stop is a regular expression metacharacter meaning match any character (with caveats, see perlretut, perlre). However, a backslash escapes the special meaning of a metacharacter so that \. matches a literal full stop. That means you are spliting on two literal full stops, which is not quite what was wanted.

$ perl -le '
> $in = q{abcdefg};
> @vals = split m{\.\.}, $in;
> print for @vals;'
abcdefg
$ perl -le '
> $in = q{abc..defg};
> @vals = split m{\.\.}, $in;
> print for @vals;'
abc
defg
$
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I hope this is of interest.