It is possible, if kissing a pope’s foot was ever practiced, it was based on Sacred Scripture:
St. Paul praised the Galatians for the respect they showed him, saying, “and though my condition was a trial to you, you did not scorn or despise me, but received me as an angel of God, as Christ Jesus.” (Gal 4:14)
And, how did the woman at the Pharisee’s house receive Christ Jesus? “And behold, a woman of the city, who was a sinner, when she learned that he was at table in the Pharisee’s house, brought an alabaster flask of ointment, and standing behind him at his feet, weeping, she began to wet his feet with her tears, and wiped them with the hair of her head, and kissed his feet, and anointed them with the ointment.” (Luke 7:37-38)
As St. Paul says elsewhere, “How beautiful are the feet of those who preach good news!” (Rom 10:13-15)