[rewboss]

It's a humorous reference to a popular song sung at Christmas.

The first verse is very short:

On the first day of Christmas,
My true love sent to me:
A partridge in a pear tree.

The second verse is a little longer:

On the second day of Christmas,
My true love sent to me:
Two turtle-doves
And a partridge in a pear tree.

For each of the 12 days of Christmas, the verses get longer until the last verse, which goes like this:

On the twelfth day of Christmas,
My true love sent to me:
Twelve drummers drumming,
Eleven pipers piping,
Ten lords a-leaping,
Nine ladies dancing,
Eight maids a-milking,
Seven swans a-swimming,
Six geese a-laying,
Five golden rings,
Four calling birds,
Three French hens,
Two turtle-doves
And a partridge in a pear tree.

Each verse basically consists of an increasingly long list of items ending with "And a partridge in a pear tree". In the article you cite, there is a similar list of items, and the author adds the "partridge in a pear tree" as a humorous remark.

Incidentally, the song is so old, nobody knows exactly what meaning lies behind each of the objects mentioned. There are many theories, but for most people it's just a very old folk song.