Symbolic kisses carried a lot of freight in medieval society -- they could be gestures of fealty, they could seal contracts, they could be gestures of friendship and amity, they could be gestures of reconciliation. The ceremony of homage you're describing is a vow of fealty from a vassal to a lord, accompanied by kneeling and clasped hands on the vassal's side; the lord sealed his acceptance of this vow by kissing the vassal on the mouth. 6th century Franks and Normans seal oaths with kisses between men of high status; men and women alike might kiss other men and other women when greeting and bidding farewell, well into the 12th and 13th centuries. (J. Russell Major's "Bastard Feudalism and the Kiss" suggests women declaring fealty to men were actively excluded from the kiss; a male proxy performed the kiss for them, because the kiss had become a codified legal act for sealing a contract, not a spontaneous outpouring of emotion. The symbolic phrases associated with fealty, stuff like "I become your [man/woman]", also had indecent and undesirable connotations of marriage when said by women toward men, connotations that were apparently not present when men said them to men.) This public and symbolic kiss carried with it tons of power dynamics and cultural baggage well into the High Middle Ages, and this baggage imposed some shades of meaning on kisses depicted in literature, even ones taking place between opposite-sex lovers and in private.

Later on this same symbolic use of kisses remained even when the romantic kiss between men and women was in full flower. In 1396, Richard II of England met with Charles VI of France in a field near Calais, looking to seal a 28-year treaty of peace with France by taking Charles VI's daughter Isabelle as a wife. The two kings crossed over to each other, shook hands, and kissed -- later upon parting they kissed again. (One English eyewitness describes another instance of contact between the two men, where the chronically ill Charles VI looked like he might faint and Richard II supported him in his arms.) These kisses were a symbolic way of sealing a deal that was itself largely symbolic -- Isabelle was six or seven years old, and Richard II would be dead before either of them would even think about consummating their union. (Richard's successor, Henry IV of England, would entertain the idea of keeping Isabelle and her dowry as wife for one of his own sons after Richard's death.) Well into the Early Modern era, kisses remained a part of some traditional gestures of fealty, and kisses between same-sex friends remained as gestures of amity and loyalty, especially on meeting and departing.

The symbolic kiss got a lot of its symbolic weight from its repetition in contexts of personal loyalty and devotion. Pilgrims kissed relics to indicate their homage and fidelity to that particular saint as well as to obtain a little intimate proximity. Medieval mystics kissed lepers, kissed each other, kissed Christ in their visions, and so on. In Christian liturgy there's talk of kisses of peace, Jesus kissing his disciples, kisses between early Christians, Judas kisses, and all manner of symbolic kisses that however ardent they might be weren't conceptualized at the time in terms of erotic desire and that even now we don't really conceptualize in terms of prolonged lip-on-lip contact or use of tongues. (Barring jokes about Judas putting on lip balm first.) The kiss of peace as initially conceptualized byl thinkers like St. Augustine was by its nature supposed to be performed non-exclusively between persons of the same sex, and it was meant to be a sign of spiritual intimacy:

After [the Lord's Prayer] comes the greeting, Peace be with you, and Christians kiss one another with a holy kiss. It's a sign of peace; what is indicated by the lips should happen in the conscience; that is, just as your lips approach the lips of your brothers or sisters, so your heart should not be withdrawn from theirs.

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None of this totally overrode or overwrote the erotic significance of kissing; on top of the vernacular practice of kissing, the imagery of erotic kisses in the Song of Solomon makes a strong counter-argument to the idea that all kisses are (or should be) chaste. There was a little bit of uneasiness about the potential for lascivious kisses squeaking in under the guise of amicable kisses, but primarily in opposite-sex kisses -- some of these symbolic kisses shifted over time from being kisses on the lips to kisses on the cheek or kisses on the hands, or were replaced outright by clasping hands. Monks and ecclesiastics became squeamish about performing kisses on women even in a clear-cut ceremonious context that could have absolved them of any accusation of lustful spontaneity. There was even unease regarding the kiss of peace exchanged in the Christian liturgy. The risks of impropriety in men kissing women and women kissing men during the kiss of peace resulted in the 13th century English church inventing the pax board -- rather than the priest kissing the congregation, and the congregation kissing each other potentially in irregular gender combos, the priest kissed the pax board, and the congregation subsequently kissed the pax board one after another.

The same-sex nature of the symbolic kiss might have put fears of lustful intentions to rest, at least until they were supplanted by anxieties about the indignity of kneeling and being forced to physically seal a vow. (Even so, that sounds like like squeamishness at a position that was seen as unnecessarily humbling, precisely the component that was deemed necessary early on, rather than fear that the contract-sealing kiss was a precursor to sodomy or might be seen as such.) Sodomites were known to kiss, but kissing was not the central act of sodomy. There are times where I think we can interpret historical kisses between men or between women in a context of potential romantic/sexual intimacy between those men and those women, but kissing between men was only sexually suspect in the context of kisses that were not on the face, such as kisses on the navel or the buttocks, or when accompanied by caresses as well as embraces. There's surprisingly little focus on the tongue as an agent in kissing, which seems like the modern distinction (moreso than even duration or gender combination) between the chaste and unchaste kiss.