The book History of the Catholic Church Volume 4 by Mourret-Thompson comments on this promise of remission: This was not a sacramental absolution, given to the hundred thousand who were present, for all their sins, without previous confession; it was the remission of the temporal penalty which was promised to repentant and pardoned sinners who should undertake the holy war. The Council of Clermont had just declared in clear terms: “Whoever, simply in the spirit of faith, without vain desires of avarice and ambition, will set out for the deliverance of the Church of God at Jerusalem, for him that journey will take the place of penance” (PL, CLXII, 717). A few months later, Urban II himself, undoubtedly to forestall misunderstandings, explained this point in a discourse to the faithful of Bologna: “Know that all who undertake the holy journey, not from motives of earthly ambition, but solely for the salvation of their souls and the deliverance of the Church, will obtain the full remission of the penance after a true and perfect confession of their sins” {PL, CLI, 483). (Cf. Schroeder, Disciplinary Decrees of the General Councils, p. 436. Tr.)
During the Crusades, the Latin clergy regarded as real martyrs, and consequently as thereby saved, the crusaders who had fallen in arms while fighting against the infidels. … Probably we should see an allusion to this belief in the words which Robert the Monk (Albert of Aachen) puts on the lips of Urban II: [note: Latin text removed here; it’s similar to the promise of remission mentioned earlier]]. At a period when a great faith was associated with great passions, the hope of these spiritual favors must have exercised a powerful influence on great criminals, who entered on the Crusade to redeem their past life.
source To me, the takeaway is that the pope clarified: remission of sins only goes to those who meet the usual conditions, including confessing your sins to a priest. Sometimes a person has no ability to do that, like if he dies in the midst of battle. In such cases the Church teaches that faith and the desire for confession is enough.