He must have had companions.
Talking with Michelangelo in 1549--that is, twenty years after the event--Busini heard from his lips this account of the flight.

"I asked Michelangelo what was the reason of his departure from Florence.

He spoke as follows: 'I was one of the Nine when the Florentine troops mustered within our lines under Malatesta Baglioni and Mario Orsini and the other generals: whereupon the Ten distributed the men along the walls and bastions, assigning to each captain his own post, with victuals and provisions; and among the rest, they gave eight pieces of artillery to Malatesta for the defence of part of the bastions at S.
Miniato.

He did not, however, mount these guns within the bastions, but below them, and set no guard.' Michelangelo, as architect and magistrate, having to inspect the lines at S.Miniato, asked Mario Orsini how it was that Malatesta treated his artillery so carelessly.
The latter answered: 'You must know that the men of his house are all traitors, and in time he too will betray this town.' These words inspired him with such terror that he was obliged to fly, impelled by dread lest the city should come to misfortune, and he together with it.

Having thus resolved, he found Rinaldo Corsini, to whom he communicated his thought, and Corsini replied lightly: 'I will go with you.' So they mounted horse with a sum of money, and road to the Gate of Justice, where the guards would not let them pass.