Yes brother it is true as Muslims we should not claim to know the unseen as that is beyond us and Allah's domain, although Allah has reviled the glorious Quran and in it he has stated that the only religion acceptable in the eyes of Allah is Islam. This is the motivation that Scholars use to back such statements.
Further more it is clearly stated in the Quran that idol worship is Haraam and a great injustices.
As far as those who will enter Jannah and Jhanam Allahu Alim(Allah knows best)!
Indeed, the religion in the sight of Allah is Islam. And those who were given the Scripture did not differ except after knowledge had come to them - out of jealous animosity between themselves. And whoever disbelieves in the verses of Allah , then indeed, Allah is swift in [taking] account.
[31:13] Recall that Luqmaan said to his son, as he enlightened him, "O my son, do not set up any idols beside Allah; idolatry is a gross injustice."
[4:48] Allah does not forgive idolatry,* but He forgives lesser offenses for whomever He wills. Anyone who sets up idols beside Allah, has forged a horrendous offense.
[4:116] Allah does not forgive idol worship (if maintained until death),* and He forgives lesser offenses for whomever He wills. Anyone who idolizes any idol beside Allah has strayed far astray.
[39:65] It has been revealed to you, and to those before you that if you ever commit idol worship, all your works will be nullified, and you will be with the losers.(Those of the hellfire)