This particular claim comes to us from the account of Shihab al-Umari, who wrote that:
This man [Mansa Musa] flooded Cairo with his benefactions. He left no court emir nor holder of a royal office without the gift of a load of gold. The Cairenes made incalculable profits out of him and his suite in buying and selling and giving and taking. They exchanged gold until they depressed its value in Egypt and caused its price to fall.
Gold was at a high price in Egypt until they came in that year. The mithqal did not go below 25 dirhams and was generally above, but from that time its value fell and it cheapened in price and has remained cheap till now. The mithqal does not exceed 22 dirhams or less. This has been the state of affairs for about twelve years until this day by reason of the large amount of gold which they brought into Egypt and spent there.
and later on al-Umari also says
He had left his country with 100 loads of gold which he spent during his pilgrimage on the tribes who lay along his route from his country to Egypt, while he was in Egypt, and again from Egypt to the Noble Hijaz and back. As a consequence he needed to borrow money in Egypt and pledged his credit with the merchants at a very high rate of gain so that they made 700 dinars profit on 300.
Now, al-Umari was not describing things he saw first hand. He visited Cairo several years after the Mansa's famous hajj (in the text he mentions "about twelve years until this day", though scholars think he didn't write down his account until 18-25 years after the hajj). Necessarily, then, al-Umari is interviewing people who were present and gathering their recollections about the event.
al-Umari also includes this anecdote about Mansa Musa's interaction with the Mamluk sultan.
From the beginning of my coming to stay in Egypt I heard talk of the arrival of this sultan Musa on his Pilgrimage and found the Cairenes eager to recount what they had seem of the Africans’ prodigal spending. I asked the emir Abu…and he told me of the opulence, manly virtues, and piety of his sultan. “When I went out to meet him {he said} that is, on behalf of the mighty sultan al-Malik al-Nasir, he did me extreme honour and treated me with the greatest courtesy. He addressed me, however, only through an interpreter despite his perfect ability to speak in the Arabic tongue. Then he forwarded to the royal treasury many loads of unworked native gold and other valuables. I tried to persuade him to go up to the Citadel to meet the sultan, but he refused persistently saying: “I came for the Pilgrimage and nothing else. I do not wish to mix anything else with my Pilgrimage.” He had begun to use this argument but I realized that the audience was repugnant to him because he would be obliged to kiss the ground and the sultan’s hand. I continue to cajole him and he continued to make excuses but the sultan’s protocol demanded that I should bring him into the royal presence, so I kept on at him till he agreed.
When we came in the sultan’s presence we said to him: ‘Kiss the ground!’ but he refused outright saying: ‘How may this be?’ Then an intelligent man who was with him whispered to him something we could not understand and he said: ‘I make obeisance to God who created me!’ then he prostrated himself and went forward to the sultan. The sultan half rose to greet him and sat him by his side. They conversed together for a long time, then sultan Musa went out. The sultan sent to him several complete suits of honour for himself, his courtiers, and all those who had come with him, and saddled and bridled horses for himself and his chief courtiers….
So, from these several anecdotes, al-Umari presents Musa as very wealthy, very pious, and conforming to ideals of what a good Muslim leader should be. However, these anecdotes also always have elements where the officials and traders are "getting the better of him". It is quite possible that he or his informants could be exaggerating parts of the story, because increasing the legend of his visit also serves to reflect glory on Cairo. The narrative also reflects glory on the Mamluk sultan, because Musa is obliged to show his respect and deference despite his purported reluctance.
TL:DR - al-Umari claims that he did. That might be the truth, but there are plausible explanations for why it is an exaggeration.
Quoted text comes from Corpus of Early Arabic Sources for West African History by Nehmia Levtzion and JFP Hopkins pp. 269-273.