Is there an official Catholic position against Halloween?
No, there isn't.
How did Halloween originate?
Believe it or not, Halloween is of Christian origin.1
By 741 there was a feast in the Church celebrating all the martyrs and saints in heaven. By 840 it was known by the title "Feast of All Saints". Pope Sixtus IV in 1484 established November 1 as a holyday of obligation and gave it both a vigil (known today as "All Hallows' Eve" or "Hallowe'en") and an eight-day period or octave to celebrate the feast. By 1955, the octave of All Saints was removed.
In England, saints or holy people are called "hallowed", hence the name "All Hallow's Day" or "Hallowmas". The evening, or "e'en" before the feast became popularly known as "All Hallows' Eve," or even shorter, "Hallowe'en."2
1. cf. Should Catholics Celebrate Halloween?; HALLOWEEN: ITS ORIGINS AND CELEBRATION | EWTN; Halloween or Samhain? | Catholic Answers; and 2. below that stand in contrast to the article linked in OP as regards the origins of Halloween.
2. Liturgical year: October: History of All Hallows' Eve | Catholic Culture. (The reader is encouraged to read the rest of the article to understand the feastday's customs in England, some of which can be seen in the current celebration of Halloween).
How a pious custom turned into what we see now with no reference to the religious aspect is what can be said as well of celebrations like Christmas, where in China, for example, it is purely secular and commercial. (Of course one need not go as far as China).
Should Catholics pay attention to what the Pope says about Halloween if he said it?
Of course because he is Papa, Father. I haven't seen any official statement on the matter but given that we are called to escape the corruption of this world, we always ought to be vigilant as regards corrupting influences. The danger of the occult cannot be underestimated or overemphasized.
Does the Catholic Church celebrate Halloween?
No she doesn't!
cf. USCCB > Calendar > Roman Liturgical Calendar: October 31, 2014 was Friday of the Thirtieth Week in Ordinary Time, November 1, 2014 Solemnity of All Saints, and November 2, 2014 The Commemoration of All the Faithful Departed (All Souls).
Halloween doesn't feature.